The English word
THUG comes from Hindi
thag (and Marathi
thak), which means "a conman, a criminal." The words likely come in turn from Sanskrit
sthaga, which means "cunning." Used with a capital T, Thug referred to a member of a professional association of robbers and assassins in India. They are mentioned in English sources as early as the 17th century, and the association was active throughout the 18th century until it was finally suppressed in the early 19th century. You can read about the history of the Thugs in this
Wikipedia article - it's really fascinating!
By the time the Thugs had been eliminated, however, the word "thug" had taken on a life of its own. Beginning in the 19th century, "thug" (with a lower-case "t") continued to be used in English to refer to a cutthroat or ruffian more generally. It's acquired yet new meanings in the world of rap and hip-hop music (e.g.,
Thug Life), as you can see from the entires in the
Urban Dictionary.
The painting below shows Thugs at work, pinning their victim down in order to strangle him:
