thief: [OE] Thief goes back to a prehistoric Germanic *theubaz, which also produced German dieb, Dutch dief, Swedish tjuf, and Danish tyv. It is not clear where this came from, although it might be related to Lithuanian tupeti ‘cower, squat’ and Latvian tupt ‘squat’, in which case it would denote etymologically ‘crouching, furtive person’. From *theubaz was derived *thiūbithō, ancestor of modern English theft. => theft
