[ ruhn-awf, -of ]
/ ˈrʌnˌɔf, -ˌɒf /
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Definition of runoff

something that drains or flows off, as rain that flows off from the land in streams.
a final contest held to determine a victor after earlier contests have eliminated the weaker contestants.
a deciding final contest held after one in which there has been no decisive victor, as between two contestants who have tied for first place.
Also called rundown. a continual or prolonged reduction, especially in quantity or supply: a runoff in bank deposits; a sharp runoff in business inventories.
Stock Exchange. the final prices appearing on the ticker after the closing bell is rung for the trading day.
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Origin of runoff

1850–55, Americanism; noun use of verb phrase run off;(def. 2, 3) see -off
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023


What is a runoff?

Runoff is liquid, especially water or rainwater, that flows off or drains away, as in The storm sewer could not hold all the runoff from the recent rains. 

This sense of runoff is often used in the context of environmental science. It often refers to water that flows into streams or back into the water supply rather than seeping into the ground. For example, when farm crops are watered, any water that is not absorbed into the ground and drains away instead is runoff.

This term comes from the verb phrase run off, which can mean to drain or flow away, as in The wastewater runs off into the stream. 

An unrelated but also common meaning of runoff refers to a competition that determines a final winner after earlier contests have narrowed down the competitors. Similarly, it can refer to a contest held to determine a winner when the initial contest did not produce one, such as when two people tie. This sense of the word is especially used in the context of political elections.

For example, a place may hold an election that features five candidates. After the election, the lowest vote-getter is removed and another election is held with the remaining candidates. This process is repeated until only two candidates are left. This final election, which finally decides the winner, is called a runoff.

Less commonly, the verb run off can mean to decide a winner through a runoff, as in The final contest will be run off at the end of the month. 

Example: Due to the use of pesticides in many industrial farms, runoff becomes a major concern for local water supplies.

Where does runoff come from?

The first records of the noun runoff come from the 1850s. It was first used in the U.S. It’s based on the sense of the verb phrase run off. 

Water runoff is a common byproduct of human activity and comes from sources such as factories, farms, and even houses. This excess water is usually contaminated in some way, such as with sewage.

Runoff elections are not common in the U.S. Only a dozen or so states use them to decide winners in state or federal elections. Other contests that use runoffs to decide a winner may use terms that reflect the type of contest it is, such as playoff for sporting events and cookoff for cooking contests.

Did you know ... ?

What are some other forms related to runoff?

  • runoffs (plural noun)

What are some synonyms for runoff?

What are some words that share a root or word element with runoff

What are some words that often get used in discussing runoff?

How is runoff used in real life?

Two of the distinct meanings of runoff are commonly used in the context of water drainage and elections.



Try using runoff!

True or False?

In the context of rainwater that doesn’t sink into the ground, runoff refers to the body of water where it goes.

How to use runoff in a sentence

British Dictionary definitions for runoff

run off

verb (adverb)
noun runoff
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Other Idioms and Phrases with runoff

run off


Escape; see run away, def. 2.


Flow off, drain, as in By noon all the water had run off the driveway. [Early 1700s]


Print, duplicate, or copy, as in We ran off 200 copies of the budget. [Late 1800s]


Decide a contest or competition, as in The last two events will be run off on Tuesday. [Late 1800s]


Also, run someone out. Force or drive someone away, as in The security guard ran off the trespassers, or They ran him out of town. [Early 1700s]


Produce or perform quickly and easily, as in After years of practice, he could run off a sermon in a couple of hours. [Late 1600s]

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.