suppletive

from The Collaborative International Dictionary of English v.0.48

Suppletive \Sup"ple*tive\, Suppletory \Sup"ple*to*ry\, a. [Cf.
   F. suppl['e]tif, LL. suppletivus, from L. supplere,
   suppletum, to fill up. See {Supply}.]
   Supplying deficiencies; supplementary; as, a suppletory oath.
   [1913 Webster]