chat-up linenoun [ C ]
uk/ˈtʃæt.ʌp ˌlaɪn/us/ˈtʃæt̬.ʌp ˌlaɪn/UK informal US come-on line informala remark that someone makes to another person to make their sexual interest known to that person and start a conversation:
"Have you been here before?" "That's one of the oldest chat-up lines I've ever heard!"