"punctuation mark consisting of two dots, one above the other, used to mark grammatical discontinuity less than that indicated by a period," 1540s, from Latin colon "part of a verse or poem," from Greek kōlon "part of a verse," literally "limb, member" (especially the leg, but also of a tree limb), also, figuratively, "a clause of a sentence," a word of uncertain etymology.
The meaning evolved in modern languages from "independent clause" to the punctuation mark that sets it off. In ancient grammar a colon was one of the larger divisions of a sentence.
"large intestine," late 14c., from Latin colon, Latinized form of Greek kolon (with a short initial -o-) "large intestine," which is of unknown origin.
bacteria inhabiting the gut of man and animals, by 1921, short for Escherichia coli (1911), named for German physician Theodor Escherich (1857-1911) with Latin genitive of colon "colon" (see colon (n.2)).