thigh (n.)
Old English þeoh, þeh, from Proto-Germanic *theuham (cognates: Old Frisian thiach, Old Dutch thio, Dutch dij, Old Norse þjo, Old High German dioh), probably literally "the thick or fat part of the leg," from PIE *teuk- from root *teue- (2) "to swell" (cognates: Lithuanian taukas, Old Church Slavonic tuku, Russian tuku "fat of animals;" Lithuanian tukti "to become fat;" Avestan tuma "fat;" Greek tylos "callus, lump," tymbos "burial mound, grave, tomb;" Old Irish ton "rump;" Latin tumere "to swell," tumulus "raised heap of earth," tumidus "swollen;"tumor "a swelling;" Middle Irish tomm "a small hill," Welsh tom "mound").