Thug
early 19th century (in thug (sense 2)): from Hindi ṭhag ‘swindler, thief’, based on Sanskrit sthagati ‘he covers or conceals’. thug (sense 1) arose in the mid 19th century.
wiktionary
From Hindi ठग(ṭhag, “swindler, fraud, cheat”), from Ashokan Prakrit *𑀞𑀕𑁆𑀕𑁆-(*ṭhagg-), from Sanskrit स्थग(sthaga, “cunning, fraudulent, to cover, to conceal”) hence स्थगति(sthagati, “he/she/it covers, he/she/it conceals”), from Proto-Indo-Aryan *stʰagáti, from Proto-Indo-European *(s)teg-(“to cover with a roof”).
Thuggee was an Indian network of secret fraternities who were engaged in murdering and robbing travellers and known for strangling their victims, operating from the 17th century (possibly as early as 13th century) to the 19th century. During British Imperial rule of India, many Indian words passed into common English, and in 1810 thug referred to members of these Indian gangs. The sense was adopted more generally as "ruffian, cutthroat" by 1839. See also English thatch, deck.
etymonline
thug (n.)
1810, "member of a gang of murderers and robbers in India who strangled their victims," from Marathi thag, thak "cheat, swindler," Hindi thag, perhaps from Sanskrit sthaga-s "cunning, fraudulent," from sthagayati "(he) covers, conceals," from PIE root *(s)teg- "to cover."
The thugs roamed about the country in bands of from 10 to 100, usually in the disguise of peddlers or pilgrims, gaining the confidence of other travelers, whom they strangled, when a favorable opportunity presented itself, with a handkerchief, an unwound turban, or a noosed cord. The shedding of blood was seldom resorted to. The motive of the thugs was not so much lust of plunder as a certain religious fanaticism. The bodies of their victims were hidden in graves dug with a consecrated pickax, and of their spoil one third was devoted to the goddess Kali, whom they worshiped. [Century Dictionary]
The more correct Indian name is phanseegur (from phansi "noose"), and the activity was described in English as far back as c. 1665. Rigorously prosecuted by the British from 1831, they were driven from existence by century's end. Transferred sense of "ruffian, cutthroat, violent lowbrow" is from 1839.
