What’s the difference between reciprocation and reciprocity? The distinction is fine but useful.
Both reciprocation and reciprocity mean “an act of return or requiting”; when one reciprocates, one responds to an action or a gesture by doing the same thing or something equivalent in form or value. These words stem from the Latin term reciprocus; the verb form, reciprocare, means “move or turn back,” “rise and fall,” or “come and go, move back and forth.” Reciprocation stems directly from Latin, while reciprocity is derived from the intermediate French term réciprocité.
The difference is that reciprocation connotes a more intimate, personal exchange, while reciprocity refers to a more formal situation, such as a political or social agreement or contract: When a person returns a favor, he or she engages in reciprocation; when two countries adhere to an agreement to exchange similar privileges or products, they are practicing reciprocity.
The adjective reciprocal refers to complementary actions by two parties (or one such action), but the word is also a noun meaning “something reciprocal to something else,” including one of a pair of numbers that, when multiplied, produce a product of 1 (such as 4 and 1/4). The verb form is reciprocate, the adverbial form is reciprocally, and the adjectival form is reciprocating. (For example, a reciprocating saw is a powered saw with a blade that moves back and forth so that the operator need only hold the tool while the motor makes the saw do the work.)