a. A substance, usually a peptide or steroid, produced by one tissue and conveyed by the bloodstream to another to effect physiological activity, such as growth or metabolism.
b. A synthetic compound that acts like a hormone in the body.
2. Any of various similar substances found in plants and insects that regulate development.
[From Greek hormōn, present participle of hormān, to urge on, from hormē, impulse; see er-1 in the Appendix of Indo-European roots.]
hor·monal (-mōnəl), hor·monic (-mŏnĭk) adj.
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