Learn Hardcore Icelandic: Flugvélin flýgur eftir hádegi.

flugvélin is the definite form of flugvél (‘airplane’). In Icelandic, the definite article attaches to the noun as a suffix. For feminine nouns like flugvél, you add -in to form the singular definite: flugvél → flugvélin. Here it’s in the nominative case because it’s the subject of the sentence.

Why is the verb flýgur used instead of a future-tense form?

Icelandic doesn’t have a separate future tense. The present tense of fljúga (‘to fly’) is flýgur, and it’s used with time expressions to talk about the future. So although the sentence means “the plane will fly after noon,” you use the present flýgur.

How do we know flýgur is from fljúga and not a regular verb ending in -ar?

fljúga is irregular. Its present 3rd person singular form changes the stem vowel and becomes flýgur, not fljúgar. Regular verbs of the -a class would form -ar endings, but fljúga follows its own pattern.

What role does eftir play in the sentence?

eftir is a preposition meaning ‘after’ when talking about time. It governs the accusative case, so it introduces the time phrase eftir hádegi (‘after noon’).

Why is it hádegi and not hádegis (genitive) or hádeginn (definite)?

Because eftir requires the accusative. hádegi is a neuter noun whose accusative singular is identical to the nominative indefinite, so it stays hádegi. You don’t use the genitive hádegis, nor the definite hádeginn in this construction.

Can I start the sentence with the time phrase? How does that affect word order?

Yes. Icelandic follows the V2 rule: the finite verb must be in the second position. If you front eftir hádegi, the verb flýgur still comes second:
“Eftir hádegi flýgur flugvélin.”
The emphasis shifts to when the action happens.

How would I say “A plane flies after noon” if I don’t mean a specific plane?

You can drop the definite suffix:
Flugvél flýgur eftir hádegi.
This can mean “A plane flies after noon.” To make it clearer you could add ein (‘one’):
Ein flugvél flýgur eftir hádegi.

Is the basic word order in this sentence the same as in English?

Yes and no. The default is Subject-Verb-Complement (SVO), so here Flugvélin (S) flýgur (V) eftir hádegi (time). That matches English. But Icelandic is strictly V2: if you move any element to the front, the finite verb must still be second—unlike English, which allows more flexibility.