Pronunciation: (hôr'mōn),[key] —n. 1. Biochem.any of various internally secreted compounds, as insulin or thyroxine, formed in endocrine glands, that affect the functions of specifically receptive organs or tissues when transported to them by the body fluids.
2. Pharm.a synthetic substance used in medicine to act like such a compound when introduced into the body.
3. Bot.Also called phytohormone. any of various plant compounds, as auxin or gibberellin, that control growth and differentiation of plant tissue.