E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Thug [a cheat].
So a religious fraternity in India was called. Their patron goddess was Devî or Kâli, wife of Siva. The Thugs lived by plunder, to obtain which they never halted at violence or even murder. In some provinces they were called stranglers (phansigars), in the Tamil tongue noosers (aritulukar), in the Canarese catgut thieves (tanti kalleru). They banded together in gangs mounted on horseback, assuming the appearance of merchants; some two or more of these gangs concerted to meet as if by accident at a given town. They then ascertained what rich merchants were about to journey, and either joined the party or lay in wait for it. This being arranged, the victim was duly caught with a lasso, plundered, and strangled. (Hindu, thaga, deceive.)