Hann er náinn fjölskyldunni.

Because náinn in this meaning takes the dative.

So the person or group someone is close to appears in the dative case:

• Hann er náinn fjölskyldunni.
• literally: He is close the-family-DAT

Compare the forms of fjölskylda:

• fjölskylda = family (nominative singular)
• fjölskyldu = family (dative singular, indefinite)
• fjölskyldunni = the family (dative singular, definite)

So fjölskyldunni is exactly the form the adjective requires here.

The dictionary form is fjölskylda, a feminine noun meaning family.

The form in the sentence is built like this:

• fjölskylda = family
• fjölskyldu = family in the dative singular
• fjölskyldunni = the family in the dative singular

A useful thing to notice is that Icelandic usually puts the onto the end of the noun, instead of using a separate word like English the.

Because it agrees with hann.

In this sentence, hann is:

• masculine
• singular
• nominative

So the adjective also appears in the matching form: náinn.

For comparison:

• Hann er náinn fjölskyldunni. = He is close to the family.
• Hún er náin fjölskyldunni. = She is close to the family.
• Það er náið samband. = It is a close relationship.

So the ending on náinn is there because Icelandic adjectives change form to match gender, number, and case.

Because Icelandic often uses case where English uses a preposition.

In English, you say:

• close to the family

In Icelandic, with náinn, you normally just use the dative directly:

• náinn fjölskyldunni

So the idea of English to is being expressed by the dative ending, not by a separate word.

Here it means emotional or social closeness.

So Hann er náinn fjölskyldunni means he has a close relationship with the family, not that he is standing physically near them.

If you want to talk about physical closeness, Icelandic usually uses other words, such as:

• nálægt = near
• nærri = near, close to

So náinn is the word for being close to someone personally.

Literally, it means the family.

But in real use, context often tells you whose family is meant. Depending on the situation, it could mean:

• his family
• her family
• their family
• some other family already known from context

Icelandic often leaves this unstated if it is already clear.

If you want to say his own family explicitly, a natural way is:

• Hann er náinn fjölskyldu sinni.

Here sinni means his own in a reflexive sense.

Normally, no—not for this standard meaning.

With náinn, Icelandic normally uses the dative without a preposition:

• Hann er náinn fjölskyldunni.

Using við here would sound unnatural or like an English-based construction.

So it is best to learn this as a pattern:

• vera náinn + dative

It is singular.

Even though a family contains several people, fjölskylda is grammatically a singular noun, just like English family.

So:

• fjölskyldunni = to the family / with the family (dative singular)

If you meant the families, the dative plural would be:

• fjölskyldunum

The basic structure is:

• Hann = subject
• er = verb
• náinn = predicative adjective
• fjölskyldunni = dative complement

So the sentence is built like:

• Subject + be + adjective + dative noun

This is a very common pattern in Icelandic.

A yes/no question would be:

• Er hann náinn fjölskyldunni? = Is he close to the family?

Sometimes, but you should be careful.

In Icelandic, náinn often simply means:

• close
• on close terms
• personally close

It does not automatically have the strong romantic or sexual sense that English intimate can have.

So in this sentence, the safest natural English idea is just:

• He is close to the family.