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, ˌpærəˈsɪtɪk /

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

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

Compare meaning

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

• parasite vs. parasitoid

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

An unusually large flare-up of cyclosporiasis, a food-borne illness caused by the cyclospora parasite, has sickened more than 10,000 people, according to the CDC.

From The Wall Street Journal ● Aug. 21, 2026

These include threats to animal health, including the New World screwworm, a flesh-eating parasite.

From Barron's ● Aug. 21, 2026

And Taylor Farms would certainly top the list for anyone glued to a toilet bowl lately, thanks to the company’s alleged indiscretion handling lettuce laced with the “explosive diarrhea” parasite.

From Salon ● Aug. 19, 2026

So are emergency department visits for diarrhea, a common symptom of cyclosporiasis, the gastrointestinal illness caused by the parasite.

From MarketWatch ● Aug. 7, 2026

Nana wouldn’t be shipped off to a home, and Charlie and Zooey wouldn’t be saddled with a little parasite neither of them was ready to care for.

From "We Are the Ants" by Shaun David Hutchinson

Handling wild game can pose food-safety risks: The Centers for Disease Control and Prevention warns that raw or undercooked wild game, including bear meat, can carry trichinella parasites, which cause trichinellosis.

From Salon ● Aug. 8, 2026

When a mosquito takes a blood meal, it also swallows any viruses or parasites living in its host’s blood.

From Slate ● Aug. 4, 2026

Marine biologists and fisheries scientists believe human influence is the main cause - impact on climate; hydropower systems that eels have to migrate through; pollution and contamination; introduction of exotic parasites; and overfishing.

From BBC ● Jul. 27, 2026

Although they travel through different levels of the ocean, they often rise to the surface to rest, regulate their body temperature, or have parasites removed.

From Science Daily ● Jul. 23, 2026

Mars has no insects, parasites, or blights to deal with, and the Hab maintains perfect growing temperature and moisture at all times.

From "The Martian" by Andy Weir