Definition of dirty

• (of behavior or especially language) characterized by obscenity or indecency; "dirty words"; "a dirty old man"; "dirty books and movies"; "boys telling dirty jokes"; "has a dirty mouth"
• vile; despicable; "a dirty (or lousy) trick"; "a filthy traitor"
• spreading pollution or contamination; especially radioactive contamination; "the air near the foundry was always dirty"; "a dirty bomb releases enormous amounts of long-lived radioactive fallout"