The Collaborative International Dictionary of English v.0.48:

Obsolete \Ob"so*lete\, a. [L. obsoletus, p. p. of obsolescere.
   See Obsolescent.]
   1. No longer in use; gone into disuse; disused; neglected;
      as, an obsolete word; an obsolete statute; -- applied
      chiefly to words, writings, or observances.
      [1913 Webster]

   2. (Biol.) Not very distinct; obscure; rudimental;
      imperfectly developed; abortive.
      [1913 Webster]

   Syn: Ancient; antiquated; old-fashioned; antique; old;
        disused; neglected. See Ancient.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Obsolete \Ob"so*lete\, v. i.
   To become obsolete; to go out of use. [R.] --Fitzed. Hall.
   [1913 Webster]

WordNet (r) 3.0 (2006):

obsolete
    adj 1: no longer in use; "obsolete words" [syn: disused,
           obsolete]

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "obsolete":
   abandoned, abjured, ago, ancient, antediluvian, antiquate,
   antiquated, antique, archaic, behind the times, blown over, by,
   bygone, bypast, dated, dead, dead and buried, deceased, defunct,
   demode, departed, deserted, discarded, discontinued, disused,
   done with, elapsed, expired, extinct, finished, forgotten, gone,
   gone glimmering, gone out, gone-by, has-been, hors de combat,
   irrecoverable, lapsed, no more, not worth saving, obsolesce,
   obsolescent, off the field, old, old hat, old-fashioned, old-time,
   old-timey, on the shelf, out, out of commission, out of date,
   out of fashion, out of gear, out of style, out of use, out-of-date,
   outdated, outmoded, outworn, over, passe, passed, passed away,
   past, past use, pensioned off, relinquished, renounced, resigned,
   retired, run out, superannuate, superannuated, superseded, unused,
   vanished, worn-out, wound up



Bouvier's Law Dictionary, Revised 6th Ed (1856):

OBSOLETE. This term is applied to those laws which have lost their efficacy,
without being repealed,
     2. A positive statute, unrepealed, can never be repealed by non-user
alone. 4 Yeates, Rep. 181; Id. 215; 1 Browne's Rep. Appx. 28; 13 Serg. &
Rawle, 447. The disuse of a law is at most only presumptive evidence that
society has consented to such a repeal; however this presumption may operate
on an unwritten law, it cannot in general act upon one which remains as a
legislative act on the statute book, because no presumption can set aside a
certainty. A written law may indeed become obsolete when the object to which
it was intended to apply, or the occasion for which it was enacted, no
longer exists. 1 P. A. Browne's R. App. 28. "It must be a very strong case,"
says Chief Justice Tilghman, "to justify the court in deciding, that an act
standing on the statute book, unrepealed, is obsolete and invalid. I will
not say that such case may not exist -- where there has been a non-user for
a great number of years; where, from a change of times and manners, an
ancient sleeping statute would do great mischief, if suddenly brought into
action; where a long, practice inconsistent with it has prevailed, and,
specially, where from other and latter statutes it might be inferred that in
the apprehension of the legislature, the old one was not in force." 13 Serg.
& Rawle, 452; Rutherf. Inst. B. 2, c. 6, s. 19; Merl. Repert. mot Desuetude.



The Devil's Dictionary (1881-1906):

OBSOLETE, adj.  No longer used by the timid.  Said chiefly of words.
A word which some lexicographer has marked obsolete is ever thereafter
an object of dread and loathing to the fool writer, but if it is a
good word and has no exact modern equivalent equally good, it is good
enough for the good writer.  Indeed, a writer's attitude toward
"obsolete" words is as true a measure of his literary ability as
anything except the character of his work.  A dictionary of obsolete
and obsolescent words would not only be singularly rich in strong and
sweet parts of speech; it would add large possessions to the
vocabulary of every competent writer who might not happen to be a
competent reader.