the secretion of an endocrine gland that is transmitted by the blood to the tissue on which it has a specific effect
"The pituitary hormone travels through the bloodstream to signal the thyroid gland to increase its metabolic rate."
Any substance produced by one tissue and conveyed by the bloodstream to another to effect physiological activity.
"The thyroid hormone travels through the bloodstream from the neck gland to regulate metabolism throughout the body."
In plain English: A hormone is a chemical messenger that travels through your blood to tell different parts of your body what to do.
"The doctor said that her hormone levels were normal for someone her age."
Usage: Use this word specifically for chemical messengers like insulin or estrogen that travel through your blood to regulate body functions, rather than general bodily fluids. It is often confused with "hormonal," which describes something related to these substances but does not refer to the specific chemicals themselves.
To treat with hormones.
"The doctor decided to treat the patient's low energy levels by administering a daily hormone injection."
The word hormone comes from Ancient Greek, where it originally described the act of setting something in motion or urging it forward. It entered English with this sense of an internal force that impels action within the body.