The Collaborative International Dictionary of English v.0.48:

Surplus \Sur"plus\, n. [F., fr. sur over + plus more. See
   Sur-, and Plus, and cf. Superplus.]
   1. That which remains when use or need is satisfied, or when
      a limit is reached; excess; overplus.
      [1913 Webster]

   2. Specifically, an amount in the public treasury at any time
      greater than is required for the ordinary purposes of the
      government.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Surplus \Sur"plus\, a.
   Being or constituting a surplus; more than sufficient; as,
   surplus revenues; surplus population; surplus words.
   [1913 Webster]

         When the price of corn falleth, men give over surplus
         tillage, and break no more ground.       --Carew.
   [1913 Webster]

WordNet (r) 3.0 (2006):

surplus
    adj 1: 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]
    n 1: a quantity much larger than is needed [syn: excess,
         surplus, surplusage, nimiety]

Moby Thesaurus II by Grady Ward, 1.0:

127 Moby Thesaurus words for "surplus":
   accessory, additional, ancillary, another, as a bonus, auxiliary,
   balance, bonus, boot, bounce, break, bump, bust, can, cashier,
   collateral, contributory, credit, de trop, deficiency, deficit,
   defrock, degrade, demote, deplume, depose, deprive, difference,
   disbar, discharge, discrepancy, disemploy, dismiss, displace,
   displume, dividend, drum out, epact, exaggeration, excess, expel,
   extra, farther, fire, for lagniappe, fresh, furlough, further,
   give the ax, give the gate, glut, gratuity, inundation, kick,
   kick upstairs, lagniappe, lay off, left, leftover, leftovers,
   let go, let out, make redundant, margin, more, net, new, odd,
   other, outstanding, over, over and above, overabundance, overage,
   overdose, overflow, overflowing, overgrowth, overkill, overmeasure,
   overmuch, overpass, overplus, overrun, overrunning, overset,
   overspreading, overstock, oversupply, pension off, plethora, plus,
   pourboire, read out of, redundancy, redundant, release, remainder,
   remaining, remanent, remove, replace, retire, sack,
   separate forcibly, something extra, spare, strip, superannuate,
   superfluity, superfluous, superiority, supernumerary, supplemental,
   supplementary, surfeit, surplusage, surviving, suspend, tip,
   to spare, turn off, turn out, ulterior, unconsumed, unfrock,
   unused