Green’s Dictionary of Slang

1. a zealous woman-chaser; a sexual athlete; also of a sexually enthusiastic woman.

1926		Maines & Grant Wise-crack Dict. 8/2: Gunner – Girl out for conquest.
1967–8		Baker et al. CUSS 132: Gunner A sexually expert male.

2. an ambitiously competitive student.

1972		Eble Campus Sl. Oct. 3: gunner – one who really works for grades in school.
2003		Urban Dict. 26 Oct. 🌐 gunner person who is competitive,overly-ambitious and substantially exceeds minimum requirements. A gunner will compromise his/her peer relationships and/or reputation among peers in order to obtain recognition and praise from his/her superiors.
2016		C. Eble UNC-CH Campus Sl. Spring 2016 5: GUNNER — one who tries hard to appear intelligent , capable, impressive—usually coming across as fake or obnoxious: ‘Jenny told the professor that she was the one in the group who suggested the topic—she’s such a gunner’.