Green’s Dictionary of Slang

champ n.

[SE champion]

1. an excellent, first-rate person, often as a form of address.

[US]T.A. Dorgan in Zwilling TAD Lex. (1993) 25: Don’t break your neck — just wait a minute and then slant over at that rather stout chicken — she’s a champ sure.
[Ire]Joyce Ulysses 142: ithacans vow pen is champ.
[US]R. Chandler ‘Pearls Are a Nuisance’ in Spanish Blood (1946) 124: A guy that can sleep it off like you is a real champ.
[US]H. Miller Sexus (1969) 323: I want to shake your hand. I want to tell you what a real champ you are.
[Aus]D. Stivens Jimmy Brockett 276: You stood up to the last one like a champ.
[Aus]‘Nino Culotta’ They’re a Weird Mob (1958) 168: All right, champ. The damsel is not in distress.
[US]E. Grogan Ringolevio 150: Kisses Kenny bestowed on Mama Rizzo for having come through like the champ she was.
[US](con. 1960s) R. Price Wanderers 43: See you later, champ.
[US]T. Wolfe Bonfire of the Vanities 286: Just fixing a hubcap, champ.
[Aus]J.J. DeCeglie Drawing Dead [ebook] Anyone who used the word ‘chief’ in a sentence was a complete fuckwit. He’d call me ‘champ’ in a second just to clinch it.

2. (drugs) a drug user who refuses to reveal their sources to the police.

[US]C. Cooper Jr Scene (1996) 61: A champ is a junkie who won’t snitch or inform, although no such animal exists.
[US]E.E. Landy Underground Dict. (1972).

3. (US campus) in stronger use of sense 1, a person who does things to excess.

[US]Eble Campus Sl. Apr. 6: like a champ – in excess or better than anyone else. ‘I’m going to sleep like a champ.’.
[US]Eble Campus Sl. Fall 2: CHAMP – someone who does something excessively.