noun, noun or participle which takes 'suru', transitive verb
verbal promise; oral agreement
A promise made by word of mouth, not written down. Often used in contrast to a written contract. Can be used as a noun or with する to mean 'to give one's word'.
口約だけでは不安なので、契約書を作成しましょう。
A verbal promise alone makes me uneasy, so let's draw up a written contract.
彼は口約したことをすぐに忘れてしまった。
He quickly forgot what he had verbally promised.