complementarity

The state or characteristic of being complementary.

"Synergy is one of the most overused words in the English language, but there is a tremendous complementarity to these organizations."

A semantic relationship between two words wherein negative use of one entails the affirmative of the other with no gradability; the relation of binary antonyms.

For complementarity, there are entailments both from affirmative sentences to the corresponding negative sentences (which is what ordinary antonymy allows) and from negative sentences to the corresponding affirmative sentences. [...] That light is on entails That light is not off. That light is not on entails That light is off.

The idea that physical phenomena may have (mutually contradictory) properties that cannot be observed simultaneously (e.g. wave-particle duality).