Thrall comes from Old English thrael ('slave, serf'), borrowed from Old Norse thraell, from Proto-Germanic *thrahilaz, perhaps related to a root meaning 'to run' (one who runs to serve). The historical chain includes Old English thrael, Old Norse thraell, and Proto-Germanic *thrahilaz. The quoted older senses, "slave, serf" and "to run", supply the semantic anchors for thrall. The formation is best read as borrowed: the word thrall carries its older form-history into a compact English lexical shape. In present English it is used as a noun, "the state of being in another's power; a slave or captive". English derivatives include thralldom and enthrall; related English forms include enthrall and thralldom. The result is a noun whose etymology preserves both the older form and the later English specialization.