The Collaborative International Dictionary of English v.0.48:

Archaic \Ar*cha"ic\, a. [Gr. 'archai:ko`s old-fashioned, fr.
   'archai^os ancient.]
   Of or characterized by antiquity or archaism; antiquated;
   obsolescent.
   [1913 Webster]

WordNet (r) 3.0 (2006):

archaic
    adj 1: so extremely old as seeming to belong to an earlier
           period; "a ramshackle antediluvian tenement";
           "antediluvian ideas"; "archaic laws" [syn:
           antediluvian, antiquated, archaic]
    2: little evolved from or characteristic of an earlier ancestral
       type; "archaic forms of life"; "primitive mammals"; "the
       okapi is a short-necked primitive cousin of the giraffe"
       [syn: archaic, primitive]

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "archaic":
   Gothic, Victorian, abandoned, abjured, antediluvian, antiquated,
   antique, behind the times, bygone, classical, dated, deserted,
   discontinued, disused, done with, fossil, fossilized, grown old,
   medieval, mid-Victorian, not worth saving, obsolescent, obsolete,
   of other times, old, old-fashioned, old-timey, old-world,
   on the shelf, out, out of use, out-of-date, outdated, outmoded,
   outworn, passe, past use, pensioned off, petrified, relinquished,
   renounced, resigned, retired, superannuate, superannuated,
   superseded, undeveloped, worn-out