call on sb/sth phr v [T] 1 also 又作 call upon to formally ask someone to do something 〔正式地〕要求〔某人做某事〕: The UN has called on both sides to start peace talks. 联合国已要求双方开始和平谈判。 2 to visit someone for a short time 〔短时间〕拜访〔某人〕: a salesman calling on customers 一个走访客户的推销员