cotangent

from WordNet (r) 3.0 (2006)

cotangent
    n 1: ratio of the adjacent to the opposite side of a right-
         angled triangle [syn: {cotangent}, {cotan}]

from The Collaborative International Dictionary of English v.0.48

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}.
   [1913 Webster]