knock out1. To render unconscious.
2. Sports To defeat (a boxing opponent) by a knockout.
3. To render useless or inoperative: The storm knocked out the phones.
4. Informal To excite or overwhelm, especially by being sexually attractive.
5. Informal To exert or exhaust (oneself or another) to the utmost: knocked herself out to be ready on time.
6. Informal To produce in abundance: The workers knocked out 500 parts in one hour.
7. To inactivate (a gene or genes) by genetic manipulation so that the resulting phenotypic effects can be observed.