"pertaining to the colon and the rectum," by 1918, from combining form of colon (n.2) + rectal.
"large intestine," late 14c., from Latin colon, Latinized form of Greek kolon (with a short initial -o-) "large intestine," which is of unknown origin.
"pertaining to or connected with the rectum," 1822, from stem of rectum + -al (1). Related: Rectally.
most colorectal cancers arise from adenomatous polyps