parasite

American  

[par-uh-sahyt] / ˈpær əˌsaɪt /

noun

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

• parasitic adjective
• parasitically adverb

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

Infected birds shed the parasite in their saliva and poo, contaminating food sources when they feed.

From BBC • Apr. 9, 2026

Michael, then aged four, was among more than 80 people who fell ill with cryptosporidiosis, a stomach infection caused by the cryptosporidium parasite, linked to a petting farm in April 2025.

From BBC • Mar. 24, 2026

The spinning crystals may help the parasite safely break down excess peroxide, reducing the risk of damage from harmful chemical reactions.

From Science Daily • Mar. 19, 2026

What starts as a parasite quickly turns into something far more lethal, emerging in stages the crew can’t anticipate — including one of the most famous and shocking scenes in movie history.

From Los Angeles Times • Mar. 19, 2026

Use of animal systemics has concentrated chiefly on control of the cattle grub, a damaging parasite of livestock.

From "Silent Spring" by Rachel Carson