v.1. To engage someone in light, casual talk, especially in order to gain his or her favor: The salesperson chatted us up for an hour before we finally decided to buy something. I chatted up the director, hoping to get a part in the film.
2. To talk amorously to someone, usually without serious intentions; flirt with someone: Many people go to the bar just to chat up the attractive bartenders. By their false smiles, we could tell they were coming over to chat us up.