parasitism

noun

par·​a·​sit·​ism ˈper-ə-sə-ˌti-zəm 

-ˌsī-, 

ˈpa-rə-

1

: the behavior of a parasite

2

: an intimate association between organisms of two or more kinds

especially : one in which a parasite obtains benefits from a host which it usually injures

3

: parasitosis

Examples of parasitism in a Sentence

Recent Examples on the Web

Monitoring also revealed the presence of complex ecological dynamics, such as parasitism by bees of the Nomada imbricata species, which lay their eggs in the nests of the host species at the expense of the original larvae. —Simone Valesini, Wired News, 30 May 2026

Iberian harvester ants were then dependent on Messor structor ants for their survival, forcing the queens to track down males of another species, which is known as sperm parasitism. —Ashley Strickland, CNN Money, 13 Sep. 2025

This life history trait is known as obligate brood parasitism. —Grrlscientist, Forbes.com, 12 Aug. 2025

Evidence of shifts in sleep and rest in birds and bats has been shown to happen when there is a risk of parasitism after dark. —Elizabeth Rayne, ArsTechnica, 2 May 2025

Word History

First Known Use

circa 1611, in the meaning defined at sense 1

Kids Definition

parasitism

noun

par·​a·​sit·​ism ˈpar-ə-sə-ˌtiz-əm 

-ˌsīt-ˌiz-

: a close association between living things of two or more kinds of which one is a parasite obtaining benefits from the other which is a host and is usually harmed in some way

Medical Definition

parasitism

noun

par·​a·​sit·​ism ˈpar-ə-sə-ˌtiz-əm  -ˌsīt-ˌiz- 

1

: an intimate association between organisms of two or more kinds

especially : one in which a parasite obtains benefits from a host which it usually injures

2

: parasitosis