약속한 것

what was promised

→ 약속하다
phrase Rare #20,474
what was promised 약속한 거 is a common conversational form with the same meaning.
KO: 네가 약속한 것을 기억해.
EN: Remember what you promised.

우리 약속한 것 알지?

You know what we promised, right?

— 레오파드 (1963)