[syn: excess, extra, redundant, spare, supererogatory, superfluous, supernumerary, surplus]
The Collaborative International Dictionary of English v.0.48:
Superfluous \Su*per"flu*ous\, a. [L. superfluus overflowing;
   super over, above + fluere to flow. See Super-, and
   Fluent.]
   More than is wanted or is sufficient; rendered unnecessary by
   superabundance; unnecessary; useless; excessive; as, a
   superfluous price. --Shak.
   [1913 Webster]
         An authority which makes all further argument or
         illustration superfluous.                --E. Everett.
   [1913 Webster]
   Superfluous interval (Mus.), an interval that exceeds a
      major or perfect interval by a semitone.
      [1913 Webster]
   Syn: Unnecessary; useless; exuberant; excessive; redundant;
        needless.
        [1913 Webster] -- Su*per"flu*ous*ly, adv. --
        Su*per"flu*ous*ness, n.
        [1913 Webster]
WordNet (r) 3.0 (2006):
superfluous
    adj 1: serving no useful purpose; having no excuse for being;
           "otiose lines in a play"; "advice is wasted words"; "a
           pointless remark"; "a life essentially purposeless";
           "senseless violence" [syn: otiose, pointless,
           purposeless, senseless, superfluous, wasted]
    2: more than is needed, desired, or required; "trying to lose
       excess weight"; "found some extra change lying on the
       dresser"; "yet another book on heraldry might be thought
       redundant"; "skills made redundant by technological advance";
       "sleeping in the spare room"; "supernumerary ornamentation";
       "it was supererogatory of her to gloat"; "delete superfluous
       (or unnecessary) words"; "extra ribs as well as other
       supernumerary internal parts"; "surplus cheese distributed to
       the needy" [syn: excess, extra, redundant, spare,
       supererogatory, superfluous, supernumerary, surplus]
Moby Thesaurus II by Grady Ward, 1.0:
73 Moby Thesaurus words for "superfluous":
   accessory, accidental, additional, adscititious, adventitious,
   aimless, appurtenant, ascititious, auxiliary, casual,
   circumstantial, collateral, contingent, de trop, dispensable,
   excess, excessive, expendable, expletive, extra, feckless,
   fortuitous, gratuitous, impotent, in excess, incidental,
   ineffective, ineffectual, inessential, left, leftover, meaningless,
   needless, net, no go, nonessential, odd, of no use, outstanding,
   over, pleonastic, pointless, prolix, purposeless, redundant,
   remaining, remanent, secondary, spare, subsidiary, superabundant,
   superadded, supererogatory, supernumerary, supervenient,
   supplemental, supplementary, surplus, surviving, tautologic,
   tautologous, to spare, unasked, unavailing, uncalled-for,
   unconsumed, unessential, unnecessary, unneeded, unused, unwanted,
   useless, verbose