Source : Webster's Revised Unabridged Dictionary (1913)

Filthy \Filth"y\, a. [Compar. {Filthier}; superl. {Filthiest}.]
   Defiled with filth, whether material or moral; nasty; dirty;
   polluted; foul; impure; obscene. ``In the filthy-mantled
   pool.'' --Shak.

         He which is filthy let him be filthy still. --Rev.
                                                  xxii. 11.

   Syn: Nasty; foul; dirty; squalid; unclean; sluttish; gross;
        vulgar; licentious. See {Nasty}.

Source : WordNet®

filthy
     adj 1: disgustingly dirty; filled or smeared with offensive matter;
            "as filthy as a pigsty"; "a foul pond"; "a nasty
            pigsty of a room" [syn: {foul}, {nasty}]
     2: vile; despicable; "a dirty (or lousy) trick"; "a filthy
        traitor" [syn: {dirty}, {lousy}]
     3: thoroughly unpleasant; "filthy (or foul or nasty or vile)
        weather we're having" [syn: {foul}, {nasty}, {vile}]
     4: characterized by obscenity; "had a filthy mouth"; "foul
        language"; "smutty jokes" [syn: {foul}, {nasty}, {smutty}]
     [also: {filthiest}, {filthier}]

filthiest
     See {filthy}