mutual relation of two or more things, parts, etc.

the act of correlating or state of being correlated.

Statistics . the degree to which two or more attributes or measurements on the same group of elements show a tendency to vary together.

Physiology . the interdependence or reciprocal relations of organs or functions.

Geology . the demonstrable equivalence, in age or lithology, of two or more stratigraphic units, as formations or members of such.

noun

difference , disassociation , disconnection , imbalance

noun

alternation , analogue , complement , correspondence , correspondent , counterpart , interaction , interchange , interconnection , interdependence , interrelation , interrelationship , match , parallel , pendant , reciprocity , relationship , connection , link , linkage , tie-in , equivalence