com ‧ ple ‧ men ‧ ta ‧ ry AC /ˌkɒmpləˈment ə ri◂, ˌkɒmplɪˈment ə ri◂ $ ˌkɑːm-/ BrE AmE adjective
1 . complementary things go well together, although they are usually different:
The computer and the human mind have different but complementary abilities.
2 . technical complementary colours of light are very different and combine to make white
3 . technical two angles that are complementary add up to 90 degrees
—complementarity /ˌkɒmpləmenˈtærəti, ˌkɒmplɪmenˈtærəti $ ˌkɑːm-/ noun [uncountable]