Definition of: hormone

(hôr′mōn) noun Physiol.
An internal secretion, produced in and by one of the endocrine glands; specifically, one of a group of complex chemical compounds evolved in one part of an organism and carried thence by the blood stream or body fluids to other parts, on which it exercises a specific physiological action. Many important hormones are now made synthetically. Compare COLYONE. See ENDOCRINE. [<Gk. hormōn, ppr. of hormaein excite]
—hor·mo·nal (hôr·mō′nəl), hor·mon·ic (hôr·mon′ik) adjective