Leigufjárhæðin, greiðsludagurinn og greiðslufyrirkomulagið eru skýr.

Because Icelandic uses compound nouns very freely. What English often expresses with several words, Icelandic often packs into one word.

Here the three main nouns are built like this:

• leigufjárhæðin = leigu-
  • fjárhæð
    • definite ending
• greiðsludagurinn = greiðslu-
  • dagur
    • definite ending
• greiðslufyrirkomulagið = greiðslu-
  • fyrirkomulag
    • definite ending

So instead of something like the amount of rent or the arrangement for payment, Icelandic often prefers one compound word.

A useful rule: in compounds like these, the last part is the main noun, and the earlier part(s) modify it.

They are the definite article attached to the end of the noun. Icelandic usually says the by adding it as a suffix rather than using a separate word.

Compare:

• leigufjárhæð → leigufjárhæðin
• greiðsludagur → greiðsludagurinn
• greiðslufyrirkomulag → greiðslufyrirkomulagið

So these forms mean:

• the rent amount
• the payment date/day
• the payment arrangement

This is very normal Icelandic.

In Icelandic compounds, the last element usually determines the gender of the whole word.

So here:

• fjárhæð is feminine → leigufjárhæð is feminine
• dagur is masculine → greiðsludagur is masculine
• fyrirkomulag is neuter → greiðslufyrirkomulag is neuter

That is why the definite forms are different:

• feminine: -in
• masculine: -urinn
• neuter: -ið

So even though the first part changes the meaning, the final noun controls the grammar.

Because the subject is plural overall.

Each noun by itself is singular:

• leigufjárhæðin
• greiðsludagurinn
• greiðslufyrirkomulagið

But when you join them with og (and), they form a compound subject:

• X, Y og Z = X, Y, and Z

That whole subject is plural, so the verb must be plural too:

• er = is
• eru = are

So eru is exactly what you would expect with three things.

This is a very common learner question, because skýr can look surprising here.

Two things are happening:

• the subject is plural because it contains three items
• the three nouns are of mixed genders and refer to things, not people

With a coordinated subject like that, Icelandic commonly uses the neuter plural form of the predicate adjective. Here, that form is skýr.

So in this sentence, skýr is not singular; it is the adjective agreeing with the whole list.

Also, because the adjective comes after eru and works as a predicate adjective (are clear), Icelandic uses the strong form here.

A helpful comparison:

• Greiðslufyrirkomulagið er skýrt. = one neuter singular thing
• ... og ... eru skýr. = several mixed-gender things

So skýr is the correct agreement form for the whole subject.

Because it is a predicate adjective, not an adjective directly attached to a noun.

In sentences with vera (to be), Icelandic works much like English:

• Húsið er stórt. = The house is big.
• Skilmálarnir eru skýrir. = The terms are clear.

So here:

• eru skýr = are clear

The adjective describes the subject through the verb, so it comes after eru.

Usually only the last part of the compound carries the grammatical inflection.

That means:

• leigu- stays fixed
• greiðslu- stays fixed
• the endings are added to or reflected in the final noun

So the grammatical behavior comes from:

• fjárhæð
• dagur
• fyrirkomulag

In this sentence, the whole compounds are nominative singular definite, because each one is part of the subject of the sentence.

This is important: even if the first part looks like another case form, it is just part of the compound. The whole word is what matters in the sentence.

No. In this sentence they are not separate words at all; they are just the first elements of compounds.

So:

• leigu- is part of leigufjárhæðin
• greiðslu- is part of greiðsludagurinn
• greiðslu- is part of greiðslufyrirkomulagið

A learner may notice that these look like oblique forms of nouns, and historically that is often relevant, but in the sentence they are best treated as fixed compound-building forms.

So when reading the sentence, do not try to parse leigu or greiðslu as separate nouns with their own role in the clause. The real grammatical units are the full compounds.