The Collaborative International Dictionary of English v.0.48:

Testosterone \Tes*tos"ter*one\ (t[e^]s*t[o^]s"t[~e]r*[=o]n), n.
   [testes + o + sterone a steroid ketone.]
   a steroid hormone (C19H28O2) produced mostly in the testes,
   which is responsible for producing the secondary sexual
   characteristics of males.
   [PJC]