Middle English, from Medieval Latin, from rectum intestinum, literally, straight intestine
First Known Use: 15th century
Medical Definition of RECTUM
: the terminal part of the intestine from the sigmoid colon to the anus
Illustration of RECTUM
End segment of the large intestine (seedigestion) in which feces accumulate just prior to discharge. It is 5–6 in. (13–15 cm) long and lined with mucous membrane. One set of muscles separates it from the anal canal; another shortens it to expel feces. The rectal walls distend as feces enter, which stimulates the urge for defecation.