turn upon somebody/something phrasal verbphr v formal a) ATTACKto suddenly attack someone, using physical violence or unpleasant words 〔用暴力或恶毒言语〕突然攻击 SYN turn on
b) if a situation, event, argument etc turns upon a particular thing or idea, it depends on that thing 取决于，依…而定 SYN turn on The court case turned upon a technicality of company law. 这起诉讼案件取决于公司法的一个细则。
→ turn upon somebody/something at turn1(PHRASAL VERB)