Green’s Dictionary of Slang

1. (US) a conversation.

1884

Donaldson Chief (LA) 27 Sept. 2/6: Let’s have a pleasant chat up on things in general.

2. the first, verbal stages of seduction; thus chat-up line, the words used.

1989		C. Jennings Mouthful of Rocks 94: [H]e had developed a series of chat-up lines based entirely around amphibious terms .
1994		I. Welsh ‘A Smart Cunt’ in Acid House 207: How could anybody fail with chat-up lines like that?
1999		(con. 1979–80) A. Wheatle Brixton Rock (2004) 162: She fended off the amorous looks and chat-up lines.
2001		I. Rankin Falls 10: George ‘Hi-Ho’ Silvers was finding out that DC Phyllida Hawes and DS Ellen Wylie weren’t about to fall for his chat-up line.
2001		OnLine Dict. of Playground Sl. 🌐 chat-up n. 1) to entice someone to have sex with you or at least go out on a date with you so you can claim to have had sex with them 2) a line used for the purposes of (1).