Þau komu ómeidd heim.

Þau is the neuter plural form of they.

In Icelandic, þau is often used:

• for a mixed-gender group
• for children
• when the group is referred to in a more general or unspecified way
• when the antecedent is a neuter plural noun

So in this sentence, þau does not necessarily mean the people are neuter in any real-world sense. It is just the correct grammatical form in certain contexts.

For comparison:

• þeir = they, masculine plural
• þær = they, feminine plural
• þau = they, neuter plural

Komu is the 3rd person plural past tense of koma, which means to come.

So:

• koma = to come
• kom = came, singular
• komu = came, plural

Here it agrees with þau, which is plural, so komu is the correct form.

Ómeidd agrees with þau in number and gender.

Since þau is neuter plural, the predicate adjective also has to be neuter plural, and that form is ómeidd.

The dictionary form is usually given as:

• ómeiddur masculine
• ómeidd feminine
• ómeitt neuter singular

But in the neuter plural, the form is also ómeidd.

So the sentence is grammatically matching:

• þau = neuter plural
• ómeidd = neuter plural

It is basically a participial adjective.

It comes from the verb meiða, meaning to injure / hurt, with the negative prefix ó-, meaning un- or not.

So:

• meiddur = injured
• ómeiddur = uninjured / unharmed

In this sentence, it behaves like an adjective describing the subject after the verb, so it is best understood as an adjective derived from a participle.

Because heim means homeward / home, with a sense of movement toward home.

By contrast, heima means at home, with no movement.

So:

• Þau komu heim = they came home
• Þau eru heima = they are at home

Since komu describes motion, heim is the right choice.

In Icelandic, words like heim often work as directional adverbs, so you do not need a separate preposition meaning to.

English says:

• go home
• come home

Icelandic does the same:

• fara heim
• koma heim

So heim already carries the idea of toward home.

Not really, at least not in how it functions in this sentence.

In Þau komu ómeidd heim, heim functions as an adverb, not as a normal noun phrase.

That is why there is:

• no article
• no adjective agreeing with it
• no obvious case-marked noun structure

It is best learned as a common directional word meaning home / homewards after verbs of movement.

Because ómeidd is closely tied to the verb as a predicate complement: it tells you the state they were in when they came.

A neutral way to understand the structure is:

• Þau = subject
• komu = finite verb
• ómeidd = complement describing the subject
• heim = directional adverb

Icelandic word order is somewhat flexible, but this order is very natural. It presents the idea roughly as:

They came, unharmed, home.

In smoother English we usually say They came home unharmed, but Icelandic often places that descriptive complement before the directional adverb.

Þ is pronounced like the th in thin, not like the th in this.

So þau begins with that voiceless th sound.

This letter is called thorn in English. Icelandic still uses it as a normal part of the alphabet.