Green’s Dictionary of Slang

G n.

1. [1920s+] (orig. US, also gee) 1000 (usu. dollars or pounds) [abbr. grand n.].

2. [1970s] (US gang) the multiple rape of a woman; usu. as pull a G, to engage in this [gangbang n. (1)].

3. [1970s–80s] (UK black) a Giro cheque.

4. [1980s] (US campus) a smart and attractive male.

5. [1980s+] (US black) a gangster.

6. [1980s+] (US black, also gee) a friend, a partner; also as a term of address or praise.

7. [1990s+] (US black) money.

8. [2000s] a G-string.

9. see G-man under G adj.1

10. see gee n.7

11. see Greek n. (8)

In compounds

G-man (n.)

1. [1940s+] a garbage man.

2. [1990s+] (drugs) a cocaine dealer.

G-note (n.)

[1930s+] (US) a $1000 note.

G-pack (n.) (also G-package) [abbr. package n. (4)]

[1990s+] (US drugs) a wholesale purchase of 100 vials of crack cocaine, which can be merchandised for $1000.

G-stack (n.)

[2010s] (US drugs) a pile of small bills worth £1000.

In phrases

G off (v.)

[1990s+] (US drugs) to make $1000 in a day’s drug dealing.

half-G (n.)

[1930s+] (US Und.) $500.

on the G [SE genuine]

[2000s] (US black) honestly, sincerely.