Answer
A HORMONE is a chemical substance secreted in small quantities by an ENDOCRINE (ductless) gland, poured DIRECTLY INTO THE BLOOD, and carried to a distant TARGET ORGAN where it regulates a specific physiological activity.
A full definition needs four elements, and each is where a mark can be lost: a CHEMICAL secreted by an ENDOCRINE gland released DIRECTLY INTO THE BLOOD — ductless, which is what distinguishes endocrine from exocrine glands acts on a distant TARGET ORGAN needed only in MINUTE quantities
Hormones are sometimes called CHEMICAL MESSENGERS, and that phrase is worth using.
THE CONTRAST with nervous control, which examiners like: nervous coordination is FAST and SHORT-LIVED, travelling along nerves to a precise point. Hormonal coordination is SLOWER but longer-lasting and more widespread, travelling in the blood to every part of the body. The two together coordinate the organism.