The Collaborative International Dictionary of English v.0.48:

Percentage \Per*cent"age\ (p[~e]r*s[e^]nt"[asl]j), n. [Per cent
   + -age, as in average. See Per, and Cent.] (Com.)
   A certain rate per cent; the allowance, duty, rate of
   interest, discount, or commission, on a hundred.
   [1913 Webster]

WordNet (r) 3.0 (2006):

percentage
    n 1: a proportion in relation to a whole (which is usually the
         amount per hundred) [syn: percentage, percent, per
         centum, pct]
    2: assets belonging to or due to or contributed by an individual
       person or group; "he wanted his share in cash" [syn: share,
       portion, part, percentage]

Moby Thesaurus II by Grady Ward, 1.0:

216 Moby Thesaurus words for "percentage":
   abatement, absolute interest, adjunct, advantage, advantageousness,
   advisability, agio, allotment, allowance, appropriateness,
   arithmetical proportion, avail, bait, bank discount, behalf,
   behoof, beneficialness, benefit, big end, bigger half, bit, bite,
   breakage, bribe, budget, capital gains, carrot, cash discount,
   chain discount, charge-off, chunk, claim, cleanup, clear profit,
   commission, common, component, concession, contingent,
   contingent interest, continued fraction, convenience,
   cross section, cut, deal, decency, deduction, depreciation,
   desirability, destiny, detachment, detail, discount, dividend,
   dividends, division, dole, drawback, earnings, easement,
   encouragement, end, equal share, equitable interest, equity,
   estate, expedience, expediency, fate, feasibility, fillip,
   filthy lucre, fitness, fittingness, fraction, fruitfulness, gain,
   gains, geometric ratio, get, gettings, gleanings, gross,
   gross profit, half, halver, harmonic proportion, helping, hoard,
   holding, improper fraction, incentive, incitement, income,
   inducement, installment, interest, invitation, item, kickback,
   killing, limitation, lot, lucre, lure, makings, measure, meed,
   mess, modicum, moiety, neat profit, net, net profit, opportuneness,
   paper profits, parcel, part, particular, payment, pelf, penalty,
   penalty clause, percent, perk, perks, perquisite, persuasive,
   pickings, piece, point, politicness, portion, premium,
   price reduction, price-cut, proceeds, profit, profitability,
   profits, proportion, propriety, provocation, prudence, quadrant,
   quantum, quarter, quota, quotum, rake-off, random sample, rate,
   ratio, ration, rebate, rebatement, receipts, reduction, refund,
   remainder, return, returns, reward, right, right of entry,
   rightness, rollback, rule of three, salvage, sample, sampling,
   seasonableness, section, sector, seemliness, segment, service,
   setoff, settlement, share, slice, small share, stake, stimulation,
   stimulative, stimulus, stock, store, strict settlement,
   subdivision, subgroup, subspecies, suitability, sweetener,
   sweetening, take, take-in, tare, time discount, timeliness, title,
   trade discount, tret, trust, underselling, use, usefulness, value,
   vested interest, wealth, whet, winnings, wisdom, worth,
   worthwhileness, write-off