groin

Your groin is the crease where the top of your leg meets your body, low down at the front. It is the spot a footballer clutches after a bad stretch, the point a tailor measures to, the place that aches when you have carried a heavy box too far.

Sport talk owns the word: a groin strain, a pulled groin, a knee to the groin. It is anatomy rather than slang — polite enough for a doctor, vague enough to let English avoid naming anything more precisely, which is why it turns up in match reports and in comedy. Builders and architects have their own groin: the sharp curved edge where two arched ceilings cross, which gives a groin vault. And in American writing groin also spells the low wall of rock or timber built out into the sea to hold the sand in place, which British writing spells groyne.