1. chemical in body: a chemical secreted by an endocrine gland or some nerve cells that regulates the function of a specific tissue or organ
2. chemical in plants: a substance synthesized by plants that regulates their growth and development
3. regulating chemical in insects: a substance produced in the body of an insect that regulates various aspects of growth and development such as the change from larva to adult
4. regulating chemical: a synthetic chemical that acts like a hormone
[Early 20th century. < Greek hormōn, present participle of horman "set in motion" < hormē "assault"]
