Skýin hverfa þegar sól og þögn mætast.

Skýin is ský + the suffixed definite article.

• ský = cloud
• skýin = the clouds

A useful thing to know is that ský is a neuter noun, and its indefinite singular and plural look the same in the nominative/accusative:

• ský = a cloud
• ský = clouds
• skýin = the clouds

So the ending -in here is what tells you this is the definite plural.

Because the subject is plural: Skýin = the clouds.

The verb hverfa agrees with that plural subject:

• skýið hverfur = the cloud disappears
• skýin hverfa = the clouds disappear

This can be confusing because hverfa is also the dictionary form (the infinitive), so here the form looks exactly like the infinitive even though it is actually the 3rd person plural present.

They are in the nominative, because they are subjects.

• Skýin is the subject of hverfa
• sól og þögn is the subject of mætast

So the structure is:

• main clause: Skýin hverfa
• subordinate clause: þegar sól og þögn mætast

Even though Icelandic has four cases, this sentence is fairly straightforward: both clauses have nominative subjects.

Because mætast is the middle form and here it means something like meet each other or come together.

That fits the sentence better than plain mæta. With two things that mutually meet, Icelandic often uses the middle form:

• Þau mætast = They meet / They meet each other

So sól og þögn mætast means that sun and silence meet one another / come together.

Yes, the active verb mæta commonly takes a dative object.

For example:

• Ég mæti vini mínum = I meet my friend

But that is not the structure used here. In sól og þögn mætast, there is no object. Instead, both nouns are part of the subject, and the verb is in the middle form. So nominative is exactly what you expect.

In other words:

• mæta + dative object = meet someone
• mætast = meet each other

Because sól og þögn is a compound subject: two nouns joined by og.

In Icelandic, just like in English, two things joined by and normally count as plural. So the verb must also be plural.

That is why the sentence has:

• sól og þögn mætast

not a singular verb.

A small extra point: just like hverfa, the form mætast can look like an infinitive, but here it is functioning as a present plural verb form.

þegar means when and introduces a subordinate clause.

So the sentence is:

• main clause: Skýin hverfa
• subordinate clause: þegar sól og þögn mætast

This matters because Icelandic main clauses often follow a verb-second pattern, but subordinate clauses introduced by words like þegar do not behave the same way. After þegar, the normal order here is:

• þegar + subject + verb

So þegar sól og þögn mætast is exactly what you would expect.

Because Icelandic often allows bare nouns where English would more naturally use the.

In a sentence like this, using sól and þögn gives a more poetic, general, or symbolic feel. It sounds less like two very specific concrete things and more like abstract forces or images.

So:

• sól og þögn feels more lyrical and open-ended
• sólin og þögnin would sound more specifically definite

Both can be grammatical in the right context, but the version in your sentence has a more literary tone.

You can move it to the front:

• Þegar sól og þögn mætast hverfa skýin.

This is a very useful Icelandic pattern to notice. When a non-subject element comes first in a main clause, the finite verb still stays in the second position. So after the fronted þegar clause, the main-clause verb comes next:

• Þegar sól og þögn mætast
  • hverfa
    • skýin

That is a classic verb-second pattern in Icelandic.

Here are the forms you would normally look up:

• Skýin → ský
• hverfa → hverfa
• þegar → þegar
• sól → sól
• og → og
• þögn → þögn
• mætast → mætast
  and it is also useful to know the related active verb mæta

That is especially helpful because Icelandic often uses inflected forms that do not immediately look different from the dictionary form.

The grammar is perfectly normal, but the style is definitely poetic or literary.

What makes it feel poetic is mainly:

• the abstract pairing sól og þögn
• the bare nouns without the article
• the image of clouds disappearing when those two things meet

So a learner should understand that this is good Icelandic, but it is not the most plain, conversational kind of sentence.