Complementation and Supplementary

noun

• The grammatical relation of a word or phrase to a predicate.
• Linguistics) a distribution of related speech sounds or forms in such a way that they only appear in different contexts. (.
  • synonyms: complementary distribution

adjective

• Functioning in a supporting capacity.
  • usage: "the main library and its auxiliary branches"
  • synonyms: auxiliary, subsidiary, supplemental
• Added to complete or make up a deficiency.
  • usage: "produced supplementary volumes"
  • synonyms: supplemental

(a.) Added to supply what is wanted; additional; being or serving as, a supplement; as, a supplemental law; a supplementary sheet or volume.