groinyoudaoicibaDictYouDict[groin 词源字典]
groin: [15] Unravelling the history of groin required a good deal of detective work, and the answer that the 19th-century etymologist Walter Skeat came up with was the rather surprising one that it is related to ground. The root on which this was formed was prehistoric Germanic *grundu-, which also produced the derivative *grundja-. This passed into Old English as grynde, which seems originally to have meant ‘depression in the ground’ (although the more extreme ‘abyss’ is its only recorded sense).

It appears to correspond to Middle English grynde ‘groin’ (‘If the pricking be in the foot, anoint the grynde with hot common oil’, Lanfranc’s Science of Surgery 1400 – evidently an example of reflexology), and the theory is that the original sense ‘depression in the ground’ became transferred figuratively to the ‘depression between the abdomen and the thighs’.

By the late 15th century grynde had become gryne, and (by the not uncommon phonetic change of /ee/ to /oi/) this metamorphosed to groin in the late 16th century. (Groyne ‘wall projecting into the sea’ [16] is a different word. It is a transferred use of the now obsolete groin ‘pig’s snout’ [14], which came via Old French groin from Latin grunnīre ‘grunt’.)
[groin etymology, groin origin, 英语词源]
groin (n.)youdaoicibaDictYouDict
"oblique depression of the body between the abdomen and thighs," 1590s, earlier grine (1530s), from Middle English grynde "groin" (c. 1400), originally "depression in the ground," from Old English grynde "abyss," perhaps also "depression, hollow," from Proto-Germanic *grundus (see ground (n.)). Altered 16c. by influence of loin or obsolete groin "snout of a pig." The architectural groin "curving edge formed by the intersection of two vaults" is from 1725.