Source : Webster's Revised Unabridged Dictionary (1913)

Foul-mouthed \Foul"-mouthed`\, a.
   Using language scurrilous, opprobrious, obscene, or profane;
   abusive.

         So foul-mouthed a witness never appeared in any cause.
                                                  --Addison.

Source : WordNet®

foul-mouthed
     adj : using foul or obscene language; "noisy foul-mouthed women
           all shouting at once" [syn: {foul-spoken}]