noun

1. that which completes or brings to perfection
2. the amount or number needed to fill or complete
3. a complete set; entirety
4. something added to complete a whole; either of two parts that complete each other
5. Gram. a word or group of words that, with the verb, completes the meaning and syntactic structure of the predicate (Ex.: foreman in “make him foreman,” paid in “he expects to get paid”)
6. Immunology a complex series of proteins in the blood plasma that acts with specific antibodies to destroy corresponding antigens, as bacteria or foreign proteins
7. Math.
   1. the number of degrees that must be added to a given angle or arc to make it equal 90 degrees
   2. the subset which must be added to any given subset to yield the original set
8. Music the difference between a given interval and the complete octave
9. Naut. all of a ship's personnel, including the officers, required to operate a ship

Etymology: ME < L complementum, that which fills up or completes < complere: see complete

transitive verb