As a Noun: 1. Behaviour which is intended to initiate a sexual relationship with someone, or at least show them that you like them very much. English = flirting. Informal English = chatting up. As a Verb or Adjective: 1. To behave as if you are sexually attracted towards someone, being especially nice and friendly towards them. English = flirt. Informal English = chat up someone. Idiomatic English = make eyes at someone. 2. To talk to someone you do not already know and to try and start a sexual relationship with them. Informal English = pick someone up.