The Collaborative International Dictionary of English v.0.48:

Ribald \Rib"ald\, a.
   Low; base; mean; filthy; obscene.
   [1913 Webster]

         The busy day,
         Waked by the lark, hath roused the ribald crows.
                                                  --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ribald \Rib"ald\, n. [OE. ribald, ribaud, F. ribaud, OF. ribald,
   ribault, LL. ribaldus, of German origin; cf. OHG hr[imac]pa
   prostitute. For the ending -ald cf. E. Herald.]
   A low, vulgar, brutal, foul-mouthed wretch; a lewd fellow.
   --Spenser. Pope.
   [1913 Webster]

         Ribald was almost a class name in the feudal system . .
         . He was his patron's parasite, bulldog, and tool . . .
         It is not to be wondered at that the word rapidly
         became a synonym for everything ruffianly and brutal.
                                                  --Earle.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ribald
    adj 1: humorously vulgar; "bawdy songs"; "off-color jokes";
           "ribald language" [syn: bawdy, off-color, ribald]
    n 1: a ribald person; someone who uses vulgar and offensive
         language

Moby Thesaurus II by Grady Ward, 1.0:

99 Moby Thesaurus words for "ribald":
   Babbitt, Fescennine, Philistine, Rabelaisian, abusive, arriviste,
   bawdy, blasphemous, blue, boor, bounder, bourgeois, cad,
   calumniatory, calumnious, churl, clown, coarse, comminatory,
   contumelious, crass, crude, cursing, damnatory, denunciatory,
   devil, dirty, dysphemistic, earthy, enfant terrible, epicier,
   epithetic, excommunicative, excommunicatory, execratory, filthy,
   foul, foul-mouthed, foul-spoken, foul-tongued, fulminatory,
   fulsome, gaudy, gross, groundling, guttersnipe, hooligan,
   ill-bred fellow, imprecatory, impure, ithyphallic, lewd, looby,
   loud, lout, low fellow, lurid, maledictory, meretricious, mischief,
   mucker, nasty, nouveau riche, obscene, offensive, parvenu, peasant,
   pornographic, profane, rapscallion, rascal, raunchy, raw, risque,
   rogue, rough, roughneck, rowdy, rude, ruffian, salacious, scalawag,
   scatologic, scurrile, scurrilous, slyboots, smoking-room, smutty,
   sultry, unchaste, unclean, unprintable, unrepeatable, upstart,
   vile, vituperative, vulgarian, vulgarist, yokel