your, his, etc. word of honour

(one's) word (of honor)

One's sincere promise or vow (about or to do something). I will be in that court to stand by your side during the trail—I give you my word of honor. After the president broke his word about lowering taxes for middle-class earners, I vowed never to vote for him again.
See also: word

your, his, etc. ˌword of ˈhonour

(British English) (American English your, his, etc. ˌword of ˈhonor) used to refer to somebody’s sincere promise: He gave me his word of honour that he’d never drink again.
See also: honour, of, word