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"buttocks," Old English ærs "tail, rump," from Proto-Germanic *arsoz (cf. Old Saxon, Old High German, Old Norse ars, Middle Dutch ærs, German Arsch "buttock"), cognate with Greek orros "tail, rump, base of the spine," Hittite arrash, Armenian or "buttock," Old Irish err "tail." Middle English had arse-winning "money obtained by prostitution" (late 14c.).