By analogy with the sinc function, define the tanc function by tanc(z) congruent {(tan z)/z | for z!=0 1 | for z = 0. auto right match Since tan z/z is not a cardinal function, the "analogy" with the sinc function is one of functional structure, not mathematical properties. It is quite possible that a better term than tanc(z), as introduced here, could be coined, although there appears to be no name previously assigned to this function. The derivative is given by (d tanc(z))/(d z) = (sec^2 z)/z - (tan z)/z^2.