under the knife UK /ˌʌndə ðə ˈnaɪf/US /ˌʌndəɹ ðə ˈnaɪf/ prepositional phrase1 •(informal) Chiefly preceded by a form of go: undergoing a surgical procedure; into surgery."I don't want to go under the knife again. I had 10 surgeries as a player and many more since," [Lenny] Dykstra said, speaking as though he still had his trademark wad of tobacco in his mouth. — 2006
