supplemental

supplement +‎ -al

supplemental (comparative more supplemental, superlative most supplemental)

1. Acting to supplement.
   • 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, →ISBN, page viii:

     The supplementary bibliography (in Vol. VI) attests to the comprehensiveness of the effort.

2. Appending.
3. Lacking a regular schedule (as in a supplemental airline).

supplemental (plural supplementals)

1. Something that supplements or adds to.
2. A requisition or article of legislation that provides additional funding for a program.