arseyoudaoicibaDictYouDict[arse 词源字典]
arse: [OE] Arse is a word of considerable antiquity, and its relatives are found practically from end to end of the geographical range of the Indo-European language family, from Old Irish err ‘tail’ in the west to Armenian or ‘rump’. Its Indo-European source was *órsos, which produced the Germanic form *arsaz: hence German arsch, Dutch aars, and, via Old English ærs, English arse.

The euphemistic American spelling ass appears to be as recent as the 1930s, although there is one isolated (British) record of it from 1860. The term wheatear, for a thrushlike European bird, is an alteration over time of a Middle English epithet ‘white arse’, after its white rump feathers.
[arse etymology, arse origin, 英语词源]
arse (n.)youdaoicibaDictYouDict
"buttocks," Old English ærs "tail, rump," from Proto-Germanic *arsoz (cognates: Old Saxon, Old High German, Old Norse ars, Middle Dutch ærs, German Arsch "buttock"), from PIE root *ors- "buttock, backside" (cognates: 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.).