noun
crotch
KRAHCH/krɑːtʃ/
The fork where two limbs or branches meet.
The trousers' crotch lies at the fork where the two legs join.

Etymology
From a word for a shepherd’s crook, crotch first meant a pitchfork, then any fork or branching point. The bodily sense applies that branching image to where the torso divides into two legs.
In context
What you're doing is putting is putting your legs in between each other. So you're crotch to crotch.
More examples
- Rainwater collects in the crotch between the two main branches.
- The arborist checks the tree's crotches for signs of decay.
- The pole rests in the crotch of a forked support.
Forms
crotch · crotches