/ˈrektəm/
Noun, pl. recta or rectums
1. The final straight portion of the large intestine in some mammals, and the gut in others. The human rectum is about 12 centimetres (4.7 in) long, and begins at the rectosigmoid junction (the end of the sigmoid colon), at the level of the third sacral vertebra or the sacral promontory depending upon what definition is used. Its caliber is similar to that of the sigmoid colon at its commencement, but it is dilated near its termination, forming the rectal ampulla. It terminates at the level of the anorectal ring (the level of the puborectalis sling) or the dentate line, again depending upon which definition is used. In humans, the rectum is followed by the anal canal, before the gastrointestinal tract terminates at the anal verge. (wikipedia.org)
2. The last portion of the large intestine (colon) that communicates with the sigmoid colon above and the anus below. The terminal section of the alimentary canal; from the sigmoid flexure to the anus.The terminal part of the large intestine which opens to the anus. (biology-online.org)
3. The terminal part of the large intestine through which feces pass. (wiktionary.org)
4. The final section of the large intestine, terminating at the anus. (Google Dictionary)
5. The terminal section of the alimentary canal; from the sigmoid flexure to the anus (wordnetweb.princeton.edu)
Word origin: From Latin intestinum rectum “straight intestine,” in contrast to the convolution of the rest of the bowels, from neuter past participle of regere “to straighten”