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]