From Middle English thral, thralle, threl, threlle, from Old English þrǣl (“thrall, slave, servant”), from Old Norse þræll (“slave”) whence the Icelandic þræll (“slave”), from Proto-Germanic *þrahilaz, *þragilaz, *þrigilaz (“runner, gofer, servant”), from Proto-Indo-European *trāgʰ- (“to pull, drag, race, run”); according to ODS probably akin to Old High German drigil, servant, to the Gothic 𐌸𐍂𐌰𐌲𐌾𐌰𐌽 (þragjan) and to the Old English þrǣġan (“to run”) 
thrall (plural thralls)
- One who is enslaved or under mind control.
- (uncountable) The state of being under the control of another person.
2017 March 27, “The Observer view on triggering article 50”, in The Observer:
- A more enlightened Conservative prime minister, better attuned to the “one nation” tradition of the party of Disraeli and Macmillan, less in thrall to Little Englanders, and less intimidated by the peculiarly vicious and Manichaean worldview of the Daily Mail, would have taken a more consensual approach.
- A shelf; a stand for barrels, etc.
- To make a thrall.