breech

1. the part of a cannon behind the bore.
2. a person's buttocks.

1. relating to or denoting presentation of a fetus in which the buttocks, rump, or legs are nearest the cervix and emerge first at birth.

   breech presentation occurs in up to 3 per cent of pregnancies at term

   my second son was breech and my doctor recommended a planned C-section

1. dress (a boy) in breeches after he had been in petticoats since birth.

   in those days it wasn't customary to breech a boy until he was about four

Old English brēc (plural of brōc, of Germanic origin; related to Dutch broek ), interpreted as a singular form. The original sense was ‘garment covering the loins and thighs’ (compare with breeches), hence ‘the buttocks’ (breech (sense 2 of the noun), mid 16th century), later ‘the hind part’ of anything.