noun

• (historical, now only in the plural or attributive) A garment whose purpose is to cover or clothe the buttocks.
  "'Lat be,' quod he, ‘it shal nat be, so theech! Thou woldest make me kisse thyn old breech, And swere it were a relik of a seint,"
• (now rare) The buttocks or backside.
  "And he made a woman for playing the whore, sit upon a great stone, on her bare breech twenty-foure houres, onely with corne and water, every three dayes, till nine dayes were past […]"
• (firearms) The part of a cannon or other firearm behind the chamber.
• (nautical) The external angle of knee timber, the inside of which is called the throat.

adv

• (obstetrics, of birth) With the hips coming out before the head.

adj

• (obstetrics) Born, or having been born, breech.

verb

• (dated, transitive) To dress in breeches. (especially) To dress a boy in breeches or trousers for the first time (the breeching ceremony).
  "[…] it occurred before I was breeched, and I was breeched at three years and a quarter old;"
• (dated, transitive) To beat or spank on the buttocks.
• (transitive) To fit or furnish with a breech.
  "to breech a gun"
• (transitive) To fasten with breeching.