Green’s Dictionary of Slang

slugger n.

[slug v.2 (1)]

1. [late 19C+] a fighter, professional or otherwise, esp. one who relies on brute force rather than skill for their conquests; a thug.

2. [1950s+] used as an affectionate term of address.

3. [1970s+] (US campus) a sexual success, a seducer.