The Collaborative International Dictionary of English v.0.48:

Ganja \Gan"ja\, n. [Hind. g[=a]njh[=a].]
   The dried hemp plant, used in India for smoking. It is
   extremely narcotic and intoxicating.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ganja
    n 1: a strong-smelling plant from whose dried leaves a number of
         euphoriant and hallucinogenic drugs are prepared [syn:
         marijuana, marihuana, ganja, Cannabis sativa]
    2: the most commonly used illicit drug; considered a soft drug,
       it consists of the dried leaves of the hemp plant; smoked or
       chewed for euphoric effect [syn: cannabis, marijuana,
       marihuana, ganja]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "ganja":
   DET, DMT, LSD, Mary Jane, STP, THC, acid, antidepressant,
   ataractic, diethyltryptamine, dimethyltryptamine, gage, grass,
   hallucinogen, hash, hashish, hay, hemp, joint, kava, marijuana,
   mescal, mescal bean, mescal button, mescaline, mind-altering drug,
   mind-blowing drug, mind-expanding drug, morning glory seeds,
   peyote, pot, psilocin, psilocybin, psychedelic, psychic energizer,
   psychoactive drug, psychochemical, psychotomimetic, reefer, roach,
   stick, tea, tranquilizer, weed