Source : Webster's Revised Unabridged Dictionary (1913)

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.

   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.

Source : WordNet®

honorarium
     n : a fee paid for a nominally free service
     [also: {honoraria} (pl)]