From Longman Dictionary of Contemporary Englishunder the knifeunder the knifeinformalCURE having a medical operation → knife
Examples from the Corpus
under the knife• Every attack was accompanied by the certain knowledge that within a couple of hours I'd be under the knife.• Again and again he goes under the knife.• Bet you didn't know Northern Ireland star Michael Hughes was under the knife several weeks ago?• Ards went under the knife last night. 