The Collaborative International Dictionary of English v.0.48:

Honorarium \Hon`o*ra"ri*um\, Honorary \Hon"or*a*ry\, n. [L.
   honorarium (sc. donum), fr. honorarius. See Honorary, a.]
   1. A fee offered to professional men for their services; as,
      an honorarium of one thousand dollars. --S. Longfellow.
      [1913 Webster]

   2. (Law) An honorary payment, usually in recognition of
      services for which it is not usual or not lawful to assign
      a fixed business price. --Heumann.
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "honorarium":
   Trinkgeld, amends, atonement, blood money, bonus, bounty, bribe,
   compensation, consideration, damages, donative, double time,
   emolument, fee, gratuity, gravy, grease, guerdon, incentive pay,
   indemnification, indemnity, inducement, lagniappe, largess,
   liberality, meed, palm oil, pay, payment, perks, perquisite,
   pourboire, premium, price, quittance, recompense, redress,
   remuneration, reparation, requital, requitement, restitution,
   retribution, return, reward, salvage, salve, satisfaction,
   smart money, solatium, something extra, sportula, sweetener, tip,
   wergild