The Collaborative International Dictionary of English v.0.48:

complementation \complementation\ n. (Linguistics)
   the grammatical relation of a word or phrase to a predicate.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

complementation
    n 1: the grammatical relation of a word or phrase to a predicate
    2: (linguistics) a distribution of related speech sounds or
       forms in such a way that they only appear in different
       contexts [syn: complementary distribution,
       complementation]