ETYM French, from Latin serus servant, slave; akin to servare to protect, preserve, observe, and perhaps originally, a client, a man under one's protection. Related to Serve.
(Medieval Europe) A person who is bound to the land and owned by the feudal lord; SYN. helot, villein.
(Homonym: surf).

ETYM Old Eng. thral, thral, Icel. thraell, perhaps through AS. thrael; akin to Swed. träl, Dan. trael, and probably to AS. thraegian to run, Goth. thragjan, Greek trechein; cf. Old High Germ. dregil, drigil, a servant.
Someone held in bondage.