Knockout vs. Knock Out
“Knockout” is a closed noun for a boxing result, elimination format, or striking person or thing, and it can also be an adjective. “Knock out” is the phrasal verb for making someone unconscious, eliminating a competitor, disabling equipment, or producing something quickly.
Use “knockout” as the noun or adjective; use “knock out” as the phrasal verb.
Key details
Choose the right form
| Meaning / situation | Form / construction | Decision |
|---|---|---|
| noun or adjective | knockout | Use one word. |
| phrasal verb | knock out | Use two words. |
Quick tests
Meaning / construction test
Is the expression naming/describing something rather than functioning as a verb?
If yes: Use “knockout.”
If no: If it is the verb, use “knock out.”
Caveat: The phrasal verb has several senses; the spelling distinction is primarily word class/function.
Examples
The boxer scored a knockout in the final round.
The noun is one word.
It was a knockout performance.
The adjective is one word.
The storm knocked out power across the district.
The verb phrase is two words.
Further guidance
Core difference
The closed form functions as a noun or adjective; the open form expresses the action.
Fast Test
If you can say “knocked out” or “knocking out,” use the two-word verb.
Sense Boundary
Both forms have several established senses, so the reliable distinction is grammatical role rather than one narrow definition.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- KNOCKOUT — English meaning (opens in a new tab)Cambridge Dictionary · Noun and adjective meanings for closed “knockout”
- KNOCK OUT — English meaning (opens in a new tab)Cambridge Dictionary · Phrasal-verb meanings for “knock out”