Entry 1 sense Webster, 1913 Cotangent /(k?-t?n"jent)/ · Co·tan·gent · IPA /ˈkoʊˌtænd͡ʒənt/ 01 n. The tangent of the complement of an arc or angle. See Illust. of Functions. 1. The tangent of the complement of an arc or angle. See Illust. of Functions.(Trig.) See: Functions