Meaning of the word "under the knife" in English

What does "under the knife" mean in English? Explore the meaning, pronunciation, and specific usage of this word with Lingoland.

under the knife

US /ˈʌndər ðə naɪf/
UK /ˈʌndə ðə naɪf/
"under the knife" picture

Idiom

undergoing a surgical operation

Example:
She had to go under the knife for an emergency appendectomy.
After years of pain, he finally decided to go under the knife to fix his knee.