Definition of "supplemental"

supplemental

adjective
comparative more supplemental, superlative most supplemental
1. Acting to supplement.
  Quotations
  The supplementary bibliography (in Vol. VI) attests to the comprehensiveness of the effort.
  1992, Rudolf M[athias] Schuster, The Hepaticae and Anthocerotae of North America: East of the Hundredth Meridian, volume V, New York, N.Y.: Columbia University Press, page viii
2. Appending.
3. Lacking a regular schedule (as in a supplemental airline).
noun
plural supplementals
1. Something that supplements or adds to.
2. A requisition or article of legislation that provides additional funding for a program.