Reciprocal

Multiplicative inverse, in mathematics, the number 1/x, which multiplied by x gives the product 1, also known as a reciprocal
Reciprocal rule, a technique in calculus for calculating derivatives of reciprocal functions
Reciprocal lattice, a basis for the dual space of covectors, in crystallography
Reciprocal (grammar), a relationship between grammatical agents
Reciprocal determinism, a theory in psychology
Reciprocal altruism, a form of symbiotic relationship in evolutionary biology
Reciprocal cross, a breeding experiment in genetics
Hybrid (biology), in genetics, the result of reciprocal crossing, also known as a reciprocal hybrid