The story
From complement + -ary. Piecewise doublet of complimentary.
Etymology from Wiktionary, CC BY-SA 4.0.
complementary
com·ple·men·ta·ryToday it means: Acting as a complement; making up a whole with something else. Full definition →
Today it means: Acting as a complement; making up a whole with something else. Full definition →
From complement + -ary. Piecewise doublet of complimentary.
Etymology from Wiktionary, CC BY-SA 4.0.