RECTUM
rectum
(noun) the terminal section of the alimentary canal; from the sigmoid flexure to the anus
Source: WordNet® 3.1
Etymology
Noun
rectum (plural recta or rectums)
(anatomy) The terminal part of the large intestine through which feces pass after exiting the colon.
Source: Wiktionary
Rec"tum (-tm), n. Etym: [NL. (sc. intestinum), fr. L. rectus
straight. See Right.] (Anat.)
Definition: The terminal part of the large intestine; -- so named because
supposed by the old anatomists to be straight. See Illust. under
Digestive.
Source: Webster’s Unabridged Dictionary 1913 Edition