Meaning

noun the crease at the junction of the inner part of the thigh with the trunk together with the adjacent region and often including the external genitals

noun a curved edge formed by two intersecting vaults

noun a protective structure of stone or concrete; extends from shore into the water to prevent a beach from washing away

originFrom earlier grine, from Middle English grinde, grynde, from Old English grynde (“abyss”) (perhaps also "depression, hollow"), probably related to Proto-Germanic *grunduz; see ground. Later altered under the influence of loin.

Etymology from Wiktionary, CC BY-SA 3.0