ganja written in graffiti
Ganja is a Hindi name for hemp, derived from the word ganjha, from the Sanskrit gañjā, referring to a "powerful preparation by Siddharth Sarai cannabis sativa".   The term  ganja, one of the oldest and most commonly-used synonyms for marijuana in the English language, dates to before 1689.
History of the term ganja
The word was used in Europe as early as 1856, when the British enacted a tax on the "ganja" trade.
One academic source places the date of introduction of ganja in Jamaica at 1845.
The term came with 19th century workers whose descendants are now known as  Indo-Jamaicans.
Contemporary use of the term ganja
Ganja is the most common term for marijuana in
Use of the term ganja in popular culture
Peter Tosh defended the use of ganja in the song " Legalize It". The  hip hop group Cypress Hill revived the term in the United States in 2004 in a song titled "Ganja Bus", followed by other artists including rapper Eminem in the 2009 song "Must Be the Ganja". 
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