complementary (adj.)

1620s, "ceremonious" (a sense now obsolete in this spelling of the word), from complement (n.) + -ary. Sense of "forming a complement, mutually completing each other's deficiencies," is attested by 1794, in reference to the calendar of the French Revolution; in reference to colors which in combination produce white light, by 1814. Earlier in the sense "completing, forming a complement" was complemental (c. 1600).