Source : Webster's Revised Unabridged Dictionary (1913)

Cotangent \Co*tan"gent\ (k?-t?n"jent), n. [For co. tangens, an
   abbrev. of L. complementi tangens. See {Tangent}.] (Trig.)
   The tangent of the complement of an arc or angle. See Illust.
   of {Functions}.

Source : WordNet®

cotangent
     n : ratio of the adjacent to the opposite side of a right-angled
         triangle [syn: {cotan}]