anus

nouns

the excretory opening at the end of the alimentary canal
anus
is derived from
anal
is a part of
the terminal section of the alimentary canal; from the sigmoid flexure to the anus
rectum
is a type of (narrower)
an aperture or hole that opens into a bodily cavity
"the orifice into the aorta from the lower left chamber of the heart"
opening, orifice, porta