Hún felur lykilinn undir mottunni.

A word-by-word breakdown is:

• Hún = she
• felur = hides / is hiding
• lykilinn = the key
• undir = under
• mottunni = the rug / the mat

So the structure is:

• subject: Hún
• verb: felur
• object: lykilinn
• prepositional phrase: undir mottunni

Felur is the 3rd person singular present tense of the verb að fela, which means to hide.

So:

• ég fel = I hide
• þú felur = you hide
• hún/hann/það felur = she/he/it hides

In this sentence, the subject is hún (she), so felur is the correct form.

It can mean both, depending on context.

Icelandic usually does not have a separate everyday verb form like English is hiding. The plain present tense often covers both:

• She hides the key under the rug
• She is hiding the key under the rug

Context tells you which is meant.

Because lykilinn means the key, while lykill means a key or key as the basic dictionary form.

Here’s the difference:

• lykill = key
• lykilinn = the key

Also, lykill changes form because it is the direct object of the verb felur. That is why you get lykilinn, not just the dictionary form lykill.

In Icelandic, the is usually attached to the end of the noun instead of being a separate word.

So:

• lykill = key
• lykilinn = the key

and

• motta = rug / mat
• mottunni = the rug / the mat

This attached the is called the suffixed definite article.

Yes. Lykilinn is in the accusative singular definite form.

That happens because it is the direct object of felur. In Icelandic, direct objects often appear in the accusative case.

So the noun lykill changes like this:

• lykill = nominative singular
• lykilinn = accusative singular definite

English mostly does not show this on nouns, but Icelandic does.

This is a very common question. The answer is that undir can take different cases depending on the meaning.

With prepositions like undir:

• accusative often shows movement toward a place
• dative often shows location in a place

Here, undir mottunni uses the dative and means the location under the rug.

Compare:

• undir mottuna = to under the rug / under the rug as a destination
• undir mottunni = under the rug as a location

So mottunni is the dative singular definite form.

Because the sentence can be understood as focusing on the place where the key is hidden, not just the motion of putting it there.

Icelandic often makes this distinction:

• if the emphasis is on putting something to a place, accusative is common
• if the emphasis is on where something is/ends up hidden, dative is common

So:

• Hún setur lykilinn undir mottuna = She puts the key under the rug.
• Hún felur lykilinn undir mottunni = She hides the key under the rug.

In the second sentence, the location of concealment is more important than the motion itself.

Mottunni is dative singular definite of motta.

A rough mini-paradigm is:

• motta = rug / mat
• mottan = the rug (nominative)
• mottuna = the rug (accusative)
• mottunni = the rug (dative)

So in undir mottunni, the preposition undir is governing the dative.

Yes. This is a very normal Icelandic sentence pattern:

• Hún = subject
• felur = verb
• lykilinn = object
• undir mottunni = prepositional phrase

So it is basically Subject – Verb – Object – Place, which feels quite natural to an English speaker.

Yes, but Icelandic has verb-second tendencies, so changes affect what sounds natural.

For example, you could front the place phrase:

• Undir mottunni felur hún lykilinn.

That is possible, but it gives a different emphasis, roughly highlighting under the rug.

The original sentence is the most neutral version.

It is tricky for English speakers.

A few helpful points:

• y in Icelandic is not like English y. It sounds more like a rounded vowel, somewhat like German ü.
• The ll in many Icelandic words is not pronounced like normal English ll.
• In lykill, that ll has a special Icelandic pronunciation that English speakers often hear as something a bit like tl.

So lykilinn is not pronounced the way an English speaker might guess from spelling.

The most important thing at first is to recognize it as the definite object form of lykill.

Usually yes, when referring to a female person.

But grammatically, Icelandic also has grammatical gender, so pronouns can match the gender of nouns in some contexts. In this sentence, though, hún straightforwardly means she.

The dictionary forms are:

• hún = she
• að fela = to hide
• lykill = key
• undir = under
• motta = rug / mat

This is useful because Icelandic words often change form in actual sentences, especially nouns and verbs.