契約 （ケイヤク） contract, compact, agreement

契機 （ケイキ） opportunity, chance, trigger, cause

幽契 （ユウケイ） secret promise made to the gods

黙契 （モッケイ） implicit agreement, tacit understanding

契る （ちぎる） to pledge, to vow, to promise, to swear, to have sexual intercourse (esp. between husband and wife), to share a bed