1. [1950s+] an erection.
2. [1980s+] the penis.
3. [1990s+] (Aus.) of a man, one who has sexual intercourse; thus mad boner, an especially keen fucker n. (1)
4. [1990s+] (Aus.) a general term of abuse, on pattern of fucker n. (3)
5. [2000s] (US) in fig. use of sense 1, an obsession.
[1990s+] to masturbate.
[2000s] to be obsessed (usu. negatively) with.