complementarity

complementary +‎ -ity.

• IPA^(key): /ˌkɒmpləmɛnˈtæɹɪti/, /ˌkɒmpləmɛnˈtɛəɹɪti/

complementarity (countable and uncountable, plural complementarities)

1. The state or characteristic of being complementary.
   • 1987 April 2, Kenneth N. Gilpin, "2 Forecasting Firms to Merge," New York Times (retrieved 1 April 2014):

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

2. (linguistics, philosophy, semantics) 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.
   • 2005, Andrew John Merrison, Aileen Bloomer, Patrick Griffiths and Christopher J. Hall, Introducing Language in Use, London: Routledge, →ISBN, page 112:

     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.