Learn Icelandic: Borunin tekur langan tíma. - The drilling takes a long time.

Borun is a feminine noun ending in -un. A handy rule for these derived nouns (and those ending in -ing) is that they do not change their spelling in the accusative or dative singular! So the indefinite form remains borun across all three cases. In this sentence, it is in the nominative case with the definite article attached: borunin (the drilling). If you needed it in the accusative definite, it would be borunina, and in the dative definite, boruninni.

Why are the words langan tíma in the accusative case here?

The verb taka (to take) forces the object that is being taken to be in the accusative case. Since the drilling is taking a long time, the phrase langan tíma is the direct object and must use accusative masculine forms.

Why does the adjective langur become langan here?

The noun tími (time) is masculine. When we need its accusative form, tími becomes tíma. The adjective must match the noun's gender, number, and case. To do this, the masculine nominative langur drops its -ur ending and adds the regular masculine accusative ending -an, giving us langan.

Both -ing and -un turn verbs into feminine nouns. Why is it borun instead of ?