To collude is to work with others secretly especially in order to do something illegal or dishonest. Collude is used as a synonym of conspire and plot.

// She is accused of colluding with known criminals.

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"Two lawsuits filed in April accuse hundreds of insurers of colluding to drop policyholders and force them onto the plan, which offers limited policies that typically cost more." — Laurence Darmiento, The Los Angeles Times, 25 June 2025

Colluding—working secretly with others to do something deceitful or illegal—is not a game, but you'd never know it if you took your cues on the meaning of collude solely from its etymology. Collude comes from the Latin verb colludere, which in turn combines the prefix com-, meaning "together," and the verb ludere, "to play." Ludere, in turn, comes from ludus, meaning "game, play, or sport." (Ludus is also the source of the adjective ludicrous and the noun interlude). Collude has a related noun—collusion—which carries the specific meaning "secret agreement or cooperation." Despite their playful history, collude and collusion have always suggested illicit trickery rather than good-natured fun.