Dirty  —adj. (-ier, -iest) 1 soiled, unclean. 2 causing dirtiness (dirty job). 3 sordid, lewd, obscene. 4 unpleasant, dishonourable, unfair (dirty trick). 5 (of weather) rough, squally. 6 (of colour) muddied, dingy. —adv. Slang 1 very (a dirty great diamond). 2 in a dirty manner (talk dirty; act dirty) (esp. In senses 3 and 4 of adj.). —v. (-ies, -ied) make or become dirty.  do the dirty on colloq. Play a mean trick on.  dirtily adv. Dirtiness n.