Icelandic builds new words by compounding — gluing existing nouns together — and it does this constantly and productively, the way English bolts words together but far more often and always as a single solid word, never with a space or a hyphen. Tölva "computer" + póstur "mail" gives tölvupóstur "email"; barn "child" + skóli "school" gives barnaskóli "primary school"; sjón "sight" + varp "casting/throwing" gives sjónvarp "television." Two facts make compounds far easier to handle than they look. First, there is an iron rule of inflection: only the last element ever changes its ending or its case, and that last element alone fixes the compound's gender. Second, the joint between the two parts often carries a hidden genitive — a fossilised "of" — so reading a compound's seam tells you the relationship between its halves. (This page is about inflecting compounds; the broader story of how new words get coined lives on the word-formation page.)
The iron rule: only the last element inflects
A compound noun inflects exactly as if it were just its final element. The first part is frozen — it never takes a case ending, never pluralises, never changes for the article. Take tölvupóstur: it declines precisely like the simple masculine póstur (a hestur-type -ar masculine), and the tölvu- sits inert at the front through the whole paradigm:
| Case | Singular | Singular + article | Plural |
|---|---|---|---|
| Nefnifall (nom.) | tölvupóstur | tölvupósturinn | tölvupóstar |
| Þolfall (acc.) | tölvupóst | tölvupóstinn | tölvupósta |
| Þágufall (dat.) | tölvupósti | tölvupóstinum | tölvupóstum |
| Eignarfall (gen.) | tölvupósts | tölvupóstsins | tölvupósta |
Read down any column and the front half tölvu- never moves; all the action — -ur, -, -i, -s, -ar, -a, -um — happens on -póstur at the back. This is liberating: you never have to learn a compound's declension as a new thing. Find the last element, decline that, and you are done. Tölvupóstur is just póstur with a label glued on the front.
Ég fékk tölvupóst frá bankanum í morgun.
I got an email from the bank this morning. Accusative singular 'tölvupóst' — only the final '-póst' inflects.
Ég er búinn að svara öllum tölvupóstunum.
I've answered all the emails. Dative plural 'tölvupóstunum' — the ending sits on '-póst', 'tölvu-' is frozen.
Hann gleymdi að senda tölvupóstinn.
He forgot to send the email. Accusative singular + article 'tölvupóstinn'.
Gender comes from the last element — always
Because the final element is the grammatical head, it alone determines the compound's gender — and this overrides whatever gender the first element has. Sjón "sight" is feminine, but sjónvarp is neuter, because its head varp is neuter: you say sjónvarpið (neuter article -ið), gott sjónvarp (neuter adjective -t). Barn "child" is neuter, but barnabók "children's book" is feminine, because its head bók is feminine: barnabókin, góð barnabók. The first element's gender is simply irrelevant.
| Compound | First element (gender) | Last element (gender) | Compound gender |
|---|---|---|---|
| sjónvarp | sjón (fem.) | varp (neut.) | neuter → sjónvarpið |
| barnabók | barn (neut.) | bók (fem.) | feminine → barnabókin |
| tölvupóstur | tölva (fem.) | póstur (masc.) | masculine → tölvupósturinn |
This is one of the most reliable shortcuts in the whole gender system: you do not need to memorise the gender of a compound separately — you derive it from the head. If you know bók is feminine, you know every -bók compound (matreiðslubók, kennslubók, barnabók) is feminine. The danger is reaching for the first element's gender instead, which is exactly backwards.
Sjónvarpið er bilað aftur.
The television is broken again. Neuter article '-ið' — the head 'varp' is neuter, so the compound is neuter.
Ég keypti skemmtilega barnabók handa frænku minni.
I bought a fun children's book for my niece. Feminine adjective 'skemmtilega' — the head 'bók' is feminine.
The three linking patterns at the seam
How the two halves are joined varies, and the link is not decorative — it usually encodes the relationship. There are three common patterns:
1. Bare stem. The first element appears in its plain stem form, nothing added: sól + skin → sólskin ("sunshine"), fót + bolti → fótbolti ("football"), vatn + glas → vatnsglas… (that last one actually takes a link — see below). The bare-stem join is common when the first element is a short, vowel-final or consonant-final stem that compounds cleanly.
2. Genitive-singular link. The first element appears in its genitive singular, so the seam carries a hidden "of." This is where the link letters -s- and -ar- come from: land (gen.sg lands) + banki → landsbanki ("national/land's bank"), sól (gen.sg sólar) + ljós → sólarljós ("sunlight," literally "sun's light"), dag (gen.sg dags) + blað → dagblað's relative dagsljós ("daylight"). Reading the -s- or -ar- at the seam tells you the first element is sitting there in the genitive — "X's Y."
3. Genitive-plural link. The first element appears in its genitive plural, typically the ending -a-, marking "of [many] X": barn (gen.pl barna) + skóli → barnaskóli ("children's school," i.e. of children), barn (gen.pl barna) + bók → barnabók ("book of children"), manna + ... The -a- link signals a plural genitive — "Y of (the) Xs."
| Link type | First element form | Example | Hidden meaning |
|---|---|---|---|
| bare stem | plain stem | sólskin (sól + skin) | sun-shine |
| genitive singular |
| landsbanki (lands + banki) | bank of the land |
| genitive singular |
| sólarljós (sólar + ljós) | light of the sun |
| genitive plural |
| barnabók (barna + bók) | book of children |
The pay-off is interpretive: when you meet an unfamiliar compound, the seam is a clue. See -a- between two nouns and you are probably looking at a genitive-plural link — barnaskóli parses transparently as "school of children." See -s- and you are likely looking at a genitive-singular link — landsbanki as "bank of the land." The link is a fossilised version of the postposed genitive you met on the genitive uses page, frozen inside a single word.
Landsbankinn opnar klukkan níu.
Landsbankinn (the National Bank) opens at nine. The '-s-' seam is the genitive singular of 'land' — 'bank of the land'; the compound inflects on '-banki'.
Barnaskólinn í hverfinu er nýbyggður.
The primary school in the neighbourhood is newly built. The '-a-' seam is the genitive plural of 'barn' — 'school of children'; gender and inflection come from 'skóli'.
Sólarljósið flæddi inn um gluggann.
The sunlight streamed in through the window. 'sólar-' is the genitive singular of 'sól' — 'light of the sun'; the neuter article '-ið' comes from the head 'ljós'.
Why English speakers slip here
English compounds famously refuse a fixed orthography — email vs e-mail vs e mail, football vs foot ball — and they inflect on the last element too (toothbrushes, not teethbrush). So the solid spelling and the inflect-the-last-element rule both have rough English parallels and rarely cause trouble. The two genuine traps are different. One is inflecting the first element: an English speaker who knows barn pluralises as börn may want to write *barnabækur with a pluralised front half — but the front half is frozen; only -bók moves, giving barnabækur with the change on the back element (bók → bækur), not the front. The other trap is reading gender off the first element: seeing sjón (feminine) and treating sjónvarp as feminine. Both errors come from the same instinct — treating the first element as if it were still a live, separate word. Inside a compound it is not. It is a frozen prefix; the grammar lives entirely at the back.
Common Mistakes
❌ Ég er búinn að svara öllum tölvunumpóstum.
Incorrect — you cannot inflect the first element 'tölvu-'. Only the final '-póst' takes endings: 'tölvupóstunum'.
✅ Ég er búinn að svara öllum tölvupóstunum.
I've answered all the emails. The front element is frozen; the ending sits on '-póst'.
❌ Sjónvarpin er biluð.
Incorrect — 'sjónvarp' is NEUTER (from the head 'varp'), so singular '-ið' / 'sjónvarpið', not the feminine form. Gender comes from the last element, not 'sjón'.
✅ Sjónvarpið er bilað.
The television is broken. Neuter, from the head 'varp'.
❌ Þetta er góður barnabók.
Incorrect — 'barnabók' is feminine (head 'bók'), so the adjective is 'góð', not the masculine 'góður'. Don't read gender off 'barn'.
✅ Þetta er góð barnabók.
This is a good children's book. Feminine, from the head 'bók'.
❌ Ég á margar barnbækur.
Incorrect — the link is the genitive plural 'barna-', so it's 'barnabækur'; and the change for the plural happens on the head ('bók → bækur'), not the front.
✅ Ég á margar barnabækur.
I have many children's books. Link '-a-' (gen.pl of barn) + plural of the head 'bók → bækur'.
❌ Ég vinn í Land banki.
Incorrect — the compound is one solid word with a genitive-singular link: 'Landsbanki'. Icelandic compounds are never written with a space.
✅ Ég vinn í Landsbankanum.
I work at the Landsbanki. One word; the '-s-' seam is the genitive of 'land', and the inflection rides on '-banki'.
Key Takeaways
- Icelandic compounds are written solid — one word, no space or hyphen: tölvupóstur, barnaskóli, sjónvarp.
- Only the final element inflects. To decline a compound, decline its last element and leave the front frozen.
- The final element fixes the gender, overriding the first: sjónvarp is neuter (from varp), barnabók is feminine (from bók).
- The seam shows one of three links: bare stem (sólskin), genitive singular with -s-/-ar- (landsbanki, sólarljós), or genitive plural with -a- (barnaskóli, barnabók) — a fossilised "of."
- The recurring error is treating the first element as a live word: don't inflect it, and don't read gender from it.
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Start learning Icelandic→Related Topics
- Grammatical Gender: Masculine, Feminine, NeuterA1 — Icelandic's three grammatical genders, the phonological clues in the nominative ending that predict gender for most nouns, the residue you must simply memorise, and how gender becomes visible through article and adjective agreement.
- Using the Genitive: Possession and BeyondB1 — What the genitive case DOES and where it sits in the sentence — the neutral postposed possessor (bók kennarans 'the teacher's book'), the partitive, governance by prepositions like til, án and vegna, and the meaningful contrast between the default postposed order and the emphatic preposed possessor (mín bók).
- Forming the Genitive Across ClassesB1 — A single reference for the genitive endings of every noun class — the most variable and error-prone case. Strong masculine -s / weak masculine -a, strong feminine -ar, weak feminine -u, neuter -s, and the overwhelmingly regular genitive plural in -a (with a -na variant for weak and some feminine nouns). Plus the i-umlaut on monosyllabic feminines (hönd → handar) and proper-name genitives.
- Strong Masculine: -ar Plural (hestur type)A2 — The largest and most productive strong masculine subclass — genitive singular -s, nominative plural -ar — drilled through hestur, dagur and the -ll/-nn stems bíll and steinn, with the u-umlaut in dögum and the bare oblique singular.
- Reading a Dictionary Entry: Class FingerprintsA2 — How an Icelandic noun is cited — nom.sg plus the genitive-singular and nominative-plural endings — and why those two extra endings are a deterministic key to its whole declension class, far more efficient to memorise than entire tables.