The state or quality of being complementary; complementarity.

What is meant by complementariness?

adj. 1. Forming or serving as a complement; completing: finally acquired the complementary volumes that made a whole set. 2. Offsetting mutual deficiencies or enhancing mutual strengths: "Creatures with complementary skills flourish in each other's presence" (Richard Dawkins).

Is it complimentary or complementary?

Complimentary with an i is used when something is free or when you give someone a compliment. Complement with an e means something that completes something else as when two things go well together.