complemental(s = adj.all) complementary, completing - acting as or providing a complement (something that completes the whole);
Derived forms noun complement₄, noun complement₆, noun complement₃

1.  Supplying, or tending to supply, a deficiency; fully completing. Prynne. [1913 Webster]

2.  Complimentary; courteous. Shak. [1913 Webster]

N  correlation, reciprocalness, reciprocity, reciprocation, mutuality, correlation, interdependence, interrelation, connection, link, association, interchange, exchange, barter, reciprocator, reprocitist, reciprocal, mutual, commutual, correlative, reciprocative, interrelated, closely related, alternate, interchangeable, interdependent, international, complemental, complementary, mutually, mutatis mutandis, vice versa, each other, one another, by turns, reciprocally, happy in our mutual help.