a. The act of knocking out.
b. The state of being knocked out.
c. A blow that knocks out an opponent.
a. A victory in boxing in which one's opponent is unable to rise from the canvas within a specified time after being knocked down or is judged too injured to continue.
b. The act of winning a boxing match in this way: won the fight by a knockout.
3. Slang A strikingly attractive or impressive person or thing.
adj. also knock-out (nŏkout′)
1. Capable of knocking someone out: a knockout punch; knockout drops put in a drink.
2. Strikingly attractive or impressive.
3. Genetics Having a specific single gene inactivated or removed by genetic manipulation: knockout mice used in an experiment.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.