Given, felt, or done in return
A curve such that the polar of each point with respect to a given conic is tangential to another curve; (also) a polygon such that the polar of each point is a side of another given polygon.
A route precisely opposite to another one embarked upon, or otherwise specified.
A pair of crosses between a male of one strain and a female of another, and vice versa
A type of flanking defence found in permanent fortifications.
A hybrid resulting from a reciprocal cross.
A ratio that is the reciprocal of a given ratio.
A spiral in which the length of the radius vector is inversely proportional to the angle through which it is turned.
Behaviour that benefits another unrelated organism, carried out in the expectation of its being reciprocated; the theory holding that behaviour of this type has evolved because is likely to increase the chances of survival or reproductive success for the apparently altruistic organism.
(Originally) an equation whose roots can be divided into pairs of numbers, each the reciprocal of the other; (equivalently) an equation which is unchanged if the variable is replaced by its reciprocal (now rare); (in later use) an equation involving a reciprocal.
Physiology inhibition of a physiological activity, especially the contraction of a muscle, by the action of an antagonist; compare reciprocal innervation.
An arrangement of nerve supply as a result of which the contraction of one muscle or muscle group is accompanied by simultaneous relaxation of an antagonistic muscle or muscle group.
Mathematics the relationship between two sequences of three numbers in geometrical progression whose middle terms are equal, the ratio of the two first terms being the reciprocal of the ratio of the two last terms; (also) proportion in which one quantity varies inversely as the other; inverse proportion.
Assimilation in which two sounds mutually affect each other.
A relation that is a mathematical statement of Onsager's principle.