Rectum

n. last section of the large intestine which ends at the anus

The rectum (from the Latin rectum intestinum, meaning straight intestine) is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. The human rectum is about 12 cm long. At its commencement its caliber is similar to that of the sigmoid colon, but near its termination it is dilated, forming the rectal ampulla.
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Rectum /rec·tum/ the distal portion of the large intestine. rec·tum n. pl. rec·tums or rec·ta The terminal portion of the large intestine, extending [more]Rectum - Community and Resources

Noun
1. the terminal section of the alimentary canal; from the sigmoid flexure to the anus
(hypernym) body part
(part-holonym) large intestine
(part-meronym) rectal artery, arteria rectalis

n. rectum, last section of the large intestine which ends at the anus