—adj. 1. soiled with dirt; foul; unclean: dirty laundry. 2. spreading or imparting dirt; soiling: dirty smoke. 3. vile; mean; sordid; contemptible: to play a dirty trick on someone. 4. obscene; pornographic; lewd: a dirty joke. 5. undesirable or unpleasant; thankless: He left the dirty work for me. 6. very unfortunate or regrettable: That's a dirty shame! 7. not fair or sportsmanlike; unscrupulous: a dirty fighter. 8. hostile, insulting, contemptuous, or resentful: She gave me a dirty look. He made a dirty crack about the cooking. 9. (of a nuclear weapon) producing a relatively large amount of radioactive fallout.
10. (of the weather) stormy; squally: It looks dirty to windward. 11. Informal.obtained through illegal or disreputable means: dirty money. 12. appearing as if soiled; dark-colored; dingy; murky.
13. Slang.using or in possession of narcotics.
14. Foreign Exchange.(of currency floats) manipulated, as by a central bank influencing or changing exchange rates (opposed to clean).
15. do (someone) dirty,Slang.to treat unfairly or reprehensibly, as by cheating or slandering.
—v.t., v.i. to make or become dirty.
—adv. 1. Informal.in a mean, unscrupulous, or underhand way: to play dirty. 2. Informal.in a lewd manner: to talk dirty.