hormone

American  

[hawr-mohn] / ˈhɔr moʊn /

noun

1. Biochemistry. 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. Pharmacology. a synthetic substance used in medicine to act like such a compound when introduced into the body.

3. Also called phytohormone.  Botany. any of various plant compounds, as auxin or gibberellin, that control growth and differentiation of plant tissue.

---

hormone British  

/ ˈhɔːməʊn /

noun

1. a chemical substance produced in an endocrine gland and transported in the blood to a certain tissue, on which it exerts a specific effect

2. an organic compound produced by a plant that is essential for growth

3. any synthetic substance having the same effects

---

hormone Scientific  

/ hôr′mōn′ /

1. A chemical substance secreted by an endocrine gland or group of endocrine cells that acts to control or regulate specific physiological processes, including growth, metabolism, and reproduction. Most hormones are secreted by endocrine cells in one part of the body and then transported by the blood to their target site of action in another part, though some hormones act only in the region in which they are secreted. Many of the principal hormones of vertebrates, such as growth hormone and thyrotropin, are secreted by the pituitary gland, which is in turn regulated by neurohormone secretions of the hypothalamus. Hormones also include the endorphins, androgens, and estrogens.

2. See more at endocrine gland

3. A substance that is synthesized by a plant part and acts to control or regulate the growth and development of the plant. The action and effectiveness of a hormone can depend on the hormone's chemical structure, its amount in relation to other hormones that have competing or opposing effects, and the ways in which it interacts with chemical receptors in various plant parts. Auxins, cytokinins, gibberellins, abscisic acid, and ethylene are plant hormones.

---

Closer Look

Among the most abundant and influential chemicals in the human body are the hormones, found also throughout the entire animal and plant kingdoms. The endocrine glands alone, including the thyroid, pancreas, adrenals, ovaries, and testes, release more than 20 hormones that travel through the bloodstream before arriving at their targeted sites. The pea-sized pituitary gland, located at the base of the brain below the hypothalamus, is considered the most crucial part of the endocrine system, producing growth hormone and hormones that control other endocrine glands. Specialized cells of the nervous system also produce hormones. The brain itself releases endorphins, hormones that act as natural painkillers. Hormones impact almost every cell and organ of the human body, regulating mood, growth, tissue function, metabolism, and sexual and reproductive function. Compared to the nervous system, the endocrine system regulates slower processes such as metabolism and cell growth, while the nervous system controls more immediate functions, such as breathing and movement. The action of hormones is a delicate balancing act, which can be affected by stress, infection, or changes in fluids and minerals in the blood. The pituitary hormones are influenced by a variety of factors, including emotions and fluctuations in light and temperature. When hormone levels become abnormal, disease can result, such as diabetes from insufficient insulin or osteoporosis in women from decreased estrogen. On the other hand, excessive levels of growth hormone may cause uncontrolled development. Treatment for hormonal disorders usually involves glandular surgery or substitution by synthetic hormones.

Other Word Forms

• hormonal adjective
• hormonic adjective

Etymology

Origin of hormone

First recorded in 1900–05; from Greek hormôn “setting in motion,” present participle of hormân “to set in motion, excite, stimulate,” from horm(ḗ) horme, with ending assimilated to -one

Explanation

Use the noun hormone to describe a message-sending chemical sent out by glands in the human body, which make you hungry or moody or ready to fight. All living organisms have hormones, though the ones in plants are very different than those in people. Hormones are part of the endocrine system, which works throughout the body to send signals we need to stay alive and healthy. A hormone is secreted in a pregnant woman when it's time for her baby to be born, for example, and hormones remind us when we need to eat. The Greek root, hormon, means "that which sets in motion."

Example Sentences

The popular medicines remove feelings of hunger by acting like a natural gut hormone that makes users feel full.

From BBC • Apr. 8, 2026

Those drugs also target the GIP hormone in addition to GLP-1.

From The Wall Street Journal • Apr. 8, 2026

Subjects in studies of six individual peptides — growth hormone releasing peptide-2, ibutamoren mesylate, ipamorelin, CJC-1295, AOD-9604 and melanotan II — experienced adverse events, including death.

From Salon • Apr. 4, 2026

CagriSema is a fixed-dose combination of two medications: cagrilintide, which mimics the natural hormone amylin, and semaglutide, the active ingredient in Novo’s Wegovy and Ozempic.

From Barron's • Apr. 1, 2026

When, for example, couples report feeling indescribably happy in each other’s presence, that’s dopamine, the pleasure hormone, doing its work.

From "The Sun Is Also a Star" by Nicola Yoon

Related Words

• condom
• diaphragm
• pill