Is it de or het zuster?

de zuster

de-word

sister

/də ˈzʏstər/

Plural

de zusters

Why de

This one you just learn — no rule points to de here.

In a sentence

Mijn zuster woont in Amsterdam.

My sister lives in Amsterdam.

More de-words

The de/het checker covers one word. The full platform covers vocabulary, grammar and all five DUO sections.