parasite

American  

[par-uh-sahyt] / ˈpær əˌsaɪt /

noun

• parasites
  plural

1. an organism that lives on or in an organism of another species, known as the host, from the body of which it obtains nutriment.

2. a person who receives support, advantage, or the like, from another or others without giving any useful or proper return, as one who lives on the hospitality of others.

   They are greedy politicians, parasites with their snouts in the public trough.

   Synonyms:

   hanger-on, sponge, leech, toady, sycophant

3. (in ancient Greece) a person who received free meals in return for amusing or impudent conversation, flattering remarks, etc.

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parasite British  

/ ˈpærəˌsaɪt /

noun

1. an animal or plant that lives in or on another (the host) from which it obtains nourishment. The host does not benefit from the association and is often harmed by it

2. a person who habitually lives at the expense of others; sponger

3. (formerly) a sycophant

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parasite Scientific  

/ păr′ə-sīt′ /

1. An organism that lives on or in a different kind of organism (the host) from which it gets some or all of its nourishment. Parasites are harmful to their hosts, although the damage they do ranges widely from minor inconvenience to debilitating or fatal disease.

2. ◆ A parasite that lives or feeds on the outer surface of the host's body, such as a louse, tick, or leech, is called an ectoparasite. Ectoparasites do not usually cause disease themselves although they are frequently a vector of disease, as in the case of ticks, which can transmit the organisms that cause such diseases as Rocky Mountain spotted fever and Lyme disease.

3. ◆ A parasite that lives inside the body of its host is called an endoparasite. Endoparasites include organisms such as tapeworms, hookworms, and trypanosomes that live within the host's organs or tissues, as well as organisms such as sporozoans that invade the host's cells.

4. See more at host

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parasite Cultural  

1. An organism that lives off or in another organism, obtaining nourishment and protection while offering no benefit in return. Human parasites are often harmful to the body and can cause diseases, such as trichinosis.

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Discover More

The term parasite is often applied to a person who takes advantage of other people and fails to offer anything in return.

Other Word Forms

Derived Forms

• parasitic
  adjective
• parasitically
  adverb

Inflected Forms

Nouns

• parasites
  plural

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Etymology

Origin of parasite

First recorded in 1530–40; from Latin parasītus, from Greek parásītos one who eats at another's table, originally an adjective: “feeding beside,” equivalent to para- + sît(os) “grain, food” + -os adjective suffix; see para- ¹

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Compare meaning

How does parasite compare to similar and commonly confused words? Explore the most common comparisons:

• parasite vs. parasitoid

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Explanation

A creature that lives off another organism is a parasite. The parasite might not hurt the host, but it doesn't do anything to help it, either. If you call someone a parasite, you are really hurling an insult! The Ancient Greeks used the word parasitos to describe someone who ate at your table but never invited you back. Some telling synonyms include leech," toady, sponge, and hanger-on." Nice, huh? Some crafty birds, such as the cowbird or cuckoo, are called social parasites, laying their eggs in other birds' nests and expecting those mamas to raise their young for them. Unfortunately, there are some people like that, too.

Example Sentences

See Examples For:

parasite parasites

The exhibition brings together original Giger artwork depicting the alien egg and an original facehugger from the 1979 film, the spidery parasite whose method of reproduction helped make “Alien” a landmark of body horror.

From Los Angeles Times ● Sep. 25, 2026

Adult flies are capable of traveling miles while searching for hosts, but infected livestock, pets, birds, and other wildlife can also help carry the parasite into new areas.

From Science Daily ● Sep. 15, 2026

Taco Bell did not have to determine how a microscopic parasite entered an international lettuce supply chain.

From Salon ● Sep. 13, 2026

The agency notes that the true number of people who have been sick with the parasite is likely to be much higher.

From BBC ● Sep. 12, 2026

Within an hour I know it contains an unknown parasite similar to cryptosporidium, but no heavy metals.

From "The Last Cuentista" by Donna Barba Higuera

For example, before vaccines kick in, sharing a litter box with another house cat risks transferring parasites.

From Los Angeles Times ● Sep. 11, 2026

The executive order comes as the Trump administration is seeking to lower record-high beef prices for consumers, driven by drought and an outbreak of parasites in US beef stocks.

From BBC ● Sep. 5, 2026

Jumping genes are genetic parasites found in bacteria, plants, animals, and humans.

From Science Daily ● Aug. 5, 2026

They’ve traveled by ground and plane, across seven different eastern U.S. states, for one purpose: to be tested for parasites, including cyclospora.

From The Wall Street Journal ● Aug. 5, 2026

As a rule, viruses, microbes, and parasites do not kill the majority of their victims—the pest that wipes out its host species has a bleak evolutionary future.

From "1491" by Charles C. Mann

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