Learn Croatian: Uvijek imamo puno dužnosti. - We always have a lot of duties.

Dužnosti is in the genitive plural case because it follows the quantity word puno (a lot of). For feminine i-declension nouns like dužnost (duty), the genitive plural ending is -i.

Wait, isn't -i also the nominative plural ending for these nouns?

Yes! For feminine i-declension nouns, the nominative plural (duties) and genitive plural (a lot of duties) are exactly the same: dužnosti. You have to rely on context, like the word puno here, to know it is in the genitive case.

How do I know that dužnost is a feminine i-declension noun rather than a masculine noun?

While most Croatian nouns ending in a consonant are masculine, nouns ending in the suffix -ost (like dužnost, radost, mogućnost) are almost always feminine. They belong to the i-declension group, which has its own specific set of endings.

Is dužnost related to the word dug (debt)?

Yes! Dužnost comes from the adjective dužan (obliged, in debt), which itself comes from dug (debt). So a dužnost is literally a duty or something you are obliged to do.