1888, from combining form of colon (n.2) + Modern Latin -stoma "opening, orifice," from Greek stoma "opening, mouth" (see stoma). Colotomy "operation of making an incision in the colon" is attested from 1860, from Greek tome "a cutting."
"orifice, small opening in an animal body," 1680s, Modern Latin, from Greek stoma (genitive stomatos) "mouth; mouthpiece; talk, voice; mouth of a river; any outlet or inlet," from PIE root *stom-en-, denoting various body parts and orifices (source also of Avestan staman- "mouth" (of a dog), Hittite shtamar "mouth," Middle Breton staffn "mouth, jawbone," Cornish stefenic "palate"). Surgical sense is attested from 1937.
<a href="https://www.etymonline.com/word/ostomy">Etymology of ostomy by etymonline</a>
Harper, D. (n.d.). Etymology of ostomy. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/ostomy