/seuh plee"sheuhn/ , n. Gram.
the use in inflection or derivation of an allomorph that is not related in form to the primary allomorph of a morpheme, as the use of better as the comparative of good.
[ 1275-1325; ME: supplementation, supplement suppletion- (s. of suppletio ) a filling up, equiv. to supplet ( us ), ptp. of supplere to make complete, ( sup- SUP- + ple-, s. of plere to fill (see FULL 1 ) + -tus ptp. suffix) + -ion- -ION ]