Green’s Dictionary of Slang

1. a pimp, a confidence trickster, one who lives by their wits.

1967		M.S. Brookins ‘Aspiration’ in Kochman Rappin’ and Stylin’ Out (1972) 381: We all proceeded toward the end of the alley with great haste. As we turned the corner, the pace automatically slowed to a crawl, for gamers are never in a hurry.
1973		D. Goines Street Players 218: Give all the gamers a drink.
2006		G. Pelecanos Night Gardener 110: He never thought Park View would gentrify [...] Not that the gamers had gone away.

2. (US campus) one who is willing to take a challenge.

1997–2000		Da Bomb 🌐 12: Gamer: Someone who is up for the challenge.
2008		D. Jenkins Franchise Babe 129: Debbie was a gamer, you had to admit. Bruises and all.