Runoff vs. Run-off vs. Run Off
“Runoff” is a noun used for an additional election and for flowing water or liquid; Cambridge also records “run-off.” “Run off” is a separate two-word phrasal verb with senses including leaving suddenly and producing copies.
Use “run off” for the verb. For the noun, “runoff” and “run-off” are both documented.
Key details
Choose the right form
| Meaning / situation | Form / construction | Decision |
|---|---|---|
| noun in the documented senses | runoff / run-off | Both closed and hyphenated noun forms are documented; follow house style consistently. |
| verb phrase | run off | Use the two-word phrasal verb. |
| treat the noun spelling as a verb spelling | do not collapse the word-class distinction | Verb uses remain two words. |
Quick tests
Meaning / construction test
Is the expression functioning as a verb?
If yes: Use “run off.”
If no: If it is a noun, “runoff” and “run-off” are both documented; follow your house style.
Caveat: The evidence supports both “runoff” and “run-off” as noun forms, so house style may determine which noun spelling is preferred.
Examples
Stormwater runoff entered the drain.
“Runoff” is a noun.
The document was prepared for a run-off vote.
The hyphenated noun/adjectival styling follows the documented noun form.
I will run off a copy before the meeting.
The action is the two-word phrasal verb.
Further guidance
Core difference
Use “run off” when the expression functions as a verb; use the documented noun form for the person, thing, event, result, or modifier.
Fast Test
If tense or inflection works naturally—such as a past or -ing form—you are using the verb and should keep “run off” as separate words.
Variant Boundary
Cambridge records both “runoff” and “run-off” as noun spellings while “run off” remains a two-word phrasal verb.
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.
- RUNOFF — English meaning (opens in a new tab)Cambridge Dictionary · Noun “runoff,” with “run-off” also documented
- RUN OFF — English meaning (opens in a new tab)Cambridge Dictionary · Two-word phrasal verb “run off” for leaving, printing, and related verb senses