de overeenkomst
de-wordagreement
/də ˈoːvərˌeːnkɔmst/
de overeenkomsten
This one you just learn — no rule points to de here.
We hebben een overeenkomst gesloten.
We have made an agreement.
The de/het checker covers one word. The full platform covers vocabulary, grammar and all five DUO sections.