Green’s Dictionary of Slang

ganja n.

[Hind. ganja, the hemp plant]

1. [1920s+] (also gagga, ganga, gange, ganj, ghanja, gunga, gunja(h)) marijuana, spec. that grown in Jamaica; thus ganja man, a marijuana dealer.

2. attrib. use of sense 1.

In compounds

ganja stick (n.) [SE stick]

[1950s] (W.I.) a device for smoking marijuana.

In phrases

black ganja (n.)

[1970s+] (drugs) dark-coloured marijuana.