1a violent person, especially a criminal:he was attacked by a gang of thugs
2 (Thug) historical a member of an organization of robbers and assassins in India. Devotees of the goddess Kali, the Thugs waylaid and strangled their victims, usually travellers, in a ritually prescribed manner. They were suppressed by the British in the 1830s.
early 19th century(in sense 2): from Hindi ṭhag 'swindler, thief', based on Sanskrit sthagati 'he covers or conceals'. sense 1 arose in the mid 19th century