Thief
Old English thīof, thēof, of Germanic origin; related to Dutch dief and German Dieb, also to theft.
wiktionary
From Middle English thef, theef, þef, from Old English þēof, from Proto-West Germanic *þeub, from Proto-Germanic *þeubaz. Spelling from Northern England, where /eːo/ became [iə] rather than [eː]. (Compare the spelling of deep from Old English deop.)
etymonline
thief (n.)
Old English þeof "thief, robber," from Proto-Germanic *theuba- (source also of Old Frisian thiaf, Old Saxon thiof, Middle Dutch and Dutch dief, Old High German diob, German dieb, Old Norse þiofr, Gothic þiufs), a word of uncertain origin.
A thief takes other people's property without their knowledge ; a robber takes it openly, whether or not resistance is offered : in a looser sense, thief is often applied to one who takes a small amount, and robber to one who takes a large amount. [Century Dictionary, 1895]
