in·​fest | \ in-ˈfest How to pronounce infest (audio) \
infested; infesting; infests

Definition of infest

transitive verb

1 : to spread or swarm in or over in a troublesome manner a slum infested with crime shark-infested waters
2 : to live in or on as a parasite

Keep scrolling for more

Other Words from infest

infestant \ in-​ˈfe-​stənt How to pronounce infest (audio) \ noun
infestation \ ˌin-​ˌfe-​ˈstā-​shən How to pronounce infest (audio) \ noun
infester \ in-​ˈfe-​stər How to pronounce infest (audio) \ noun

Synonyms for infest


Visit the Thesaurus for More 

Examples of infest in a Sentence

in desperation, we called in an exterminator because the house was infested with ants
Recent Examples on the Web Mealybugs feed on plants and will infest many different types of houseplants and quickly spread through your collection. Tim Johnson,, "Mealybugs can put houseplants in a sticky situation — here’s how to get rid of them," 27 Dec. 2020 The familiar holiday species often infest stately trees such as oaks or poplar: In winter, when these trees are leafless, the parasites’ green, Truffula-like clumps are easy to spot dotting their host tree’s branches. Rachel Ehrenberg, Smithsonian Magazine, "The Biology of Mistletoe," 23 Dec. 2020 Many bark beetles infest already dead or dying trees, but some, like the mountain pine beetle, attack living ones. Hillary Rosner, National Geographic, "A tiny pest helped stoke this year’s devastating wildfires," 1 Oct. 2020 Fresh fruit was also a no-no, lest northern bugs infest southern plants or vice versa. Elisabeth Eaves, Wired, "The Pandemic Closed Borders—and Stirred a Longing for Home," 1 Oct. 2020 Fortunately, rats, which otherwise infest Paris, did not move into the crypt. Elaine Sciolino, Smithsonian Magazine, "The Notre-Dame Crypt Reopens for the First Time Since the Fire," 9 Sep. 2020 The nematodes will survive in the root nodules for long periods and will readily infest new garden areas through spreading of the compost., "Calvin Finch: It’s time for San Antonio tomato gardeners to start over with fall plants," 18 June 2020 It is most commonly carried by the black-legged or deer tick and can infest humans and pets. Kaleb A. Brown, Detroit Free Press, "Mobile app takes aim at the bane of Michigan summers — ticks and Lyme disease," 17 June 2020 This is a quick way to improvise a hammock to get off the ground in wet or bug-infested environments. Popular Science, "Fifteen survival shelters that can save your life," 28 May 2020

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'infest.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

See More

First Known Use of infest

1602, in the meaning defined at sense 1

History and Etymology for infest

French infester, from Latin infestare, from infestus hostile

Keep scrolling for more

Learn More about infest

Statistics for infest

Cite this Entry

“Infest.” Dictionary, Merriam-Webster, Accessed 19 Apr. 2021.

Style: MLA
MLACheck Mark Icon ChicagoCheck Mark Icon APACheck Mark Icon Merriam-WebsterCheck Mark Icon

Keep scrolling for more

More Definitions for infest



English Language Learners Definition of infest

of something harmful or unwanted : to be in or over (a place, an animal, etc.) in large numbers


in·​fest | \ in-ˈfest How to pronounce infest (audio) \
infested; infesting

Kids Definition of infest

: to spread or swarm in or over in a harmful manner Termites infested the tree.
in·​fest | \ in-ˈfest How to pronounce infest (audio) \

Medical Definition of infest

: to live in or on as a parasite the flea that infests cats horses infested with worms — compare infect

Keep scrolling for more

Comments on infest

What made you want to look up infest? Please tell us where you read or heard it (including the quote, if possible).


Test Your Vocabulary

The Exceptions Quiz III

  • one green toy robot amidst many red toy robots
  • Which of these words does not mean "nonsense"?
True or False

Test your knowledge - and maybe learn something along the way.

Universal Daily Crossword

A daily challenge for crossword fanatics.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!