Learn Hardcore Icelandic: Vindurinn blæs austur yfir hafið.

vindurinn is in the nominative case because it’s the subject of the sentence. Icelandic marks definiteness by adding a suffix: the indefinite vindur (wind) becomes the definite vindurinn (the wind) with -inn attached.

Why is the verb blæs spelled with æ and ending in -s?

The verb root is blæsa (to blow). In the present tense, third person singular, it changes to blæs. Here’s how it works:

æ is part of the root vowel
-s marks “he/she/it blows”

What part of speech is austur, and why isn’t it declined?

austur is an adverb meaning “eastward” or “to the east.” Adverbs in Icelandic do not change form for case, number, or gender, so austur stays the same.

Why is yfir used here, and which case does it govern?

yfir is a preposition meaning “over” or “across.” In this sense, it governs the accusative case. That’s why the noun following it is in the accusative.

Why does hafið end in -ið, and what case is it?

haf (sea) is a neuter noun. To make it definite, we add -ið, giving hafið = “the sea.” Because it’s the object of yfir, it’s in the accusative, but for neuter nouns the nominative and accusative forms look identical.

How is the word order in this sentence determined?

Icelandic generally follows a verb-second (V2) principle in main clauses:

The subject vindurinn comes first.
The finite verb blæs is second.
The rest (austur yfir hafið) follows in logical order: adverb (austur) + prepositional phrase (yfir hafið).

How would you translate Vindurinn blæs austur yfir hafið into natural English?

A natural translation is “The wind blows east across the sea.” You could also say “The wind is blowing eastward over the ocean.”