The Collaborative International Dictionary of English v.0.48:

Unchaste \Un*chaste"\, a.
   Not chaste; not continent; lewd. -- Un*chaste"ly, adv. --
   Un*chaste"ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unchaste
    adj 1: not chaste; "unchaste conduct" [ant: chaste]

Moby Thesaurus II by Grady Ward, 1.0:

89 Moby Thesaurus words for "unchaste":
   Adamic, Cyprian, Cyrenaic, Fescennine, Rabelaisian, appetitive,
   backsliding, bawdy, bent on pleasure, besmirched, blue, carnal,
   debased, defiled, dirty, easy, epicurean, erring, fallen, filthy,
   fleshly, foul, foul-mouthed, foul-spoken, foul-tongued, frail,
   fulsome, hedonistic, immodest, immoral, impure, indecent, infirm,
   ithyphallic, lapsed, lascivious, lecherous, lewd, light, loose,
   lurid, luxurious, luxury-loving, maculate, nasty, obscene,
   of easy virtue, offensive, peccable, pleasure-bent,
   pleasure-seeking, pornographic, postlapsarian, prodigal,
   promiscuous, raunchy, recidivist, recidivistic, ribald, salacious,
   scurrile, scurrilous, sensual, smirched, smoking-room, smutty,
   soiled, sullied, sultry, sybaritic, tainted, unangelic, unclean,
   uncleanly, ungodly, ungood, unprintable, unrepeatable, unrighteous,
   unsaintly, unvirginal, unvirtuous, vile, virtueless, voluptuous,
   wanton, wayward, weak, whorish