vouch
/vautʃ; vaʊtʃ/ v[Ipr]
1 ~ for sb/sth take responsibility for or express confidence in (a person, his behaviour, etc); guarantee 为（某人、 其行为等）担保或作证; 保证
I can vouch for him/his honesty. 我可以为他[他的诚实]作担保.
2 ~ for sth confirm (a claim, etc) by producing evidence or drawing on one's own experience（提供证据或现身说法）确定（某权利要求等）
Experts vouch for the painting's authenticity. 由专家确认该画是否为真迹.