noun ·Rare ·Advanced level

Definitions

Noun

1. 1
   A hormone, related to serotonin, that is secreted by the pineal gland, and stimulates colour change in the skin of reptiles, and is involved in the sleep and wake and reproductive cycles in mammals. uncountable, usually

   "How exactly melatonin relates to sleep is still not understood."

2. 2
   hormone secreted by the pineal gland wordnet
3. 3
   Any material similar in its chemistry and effect to the natural hormone. uncountable, usually

Example

More examples

"The pineal gland secretes melatonin."

Etymology

From mela- + tone + -in, ultimately from Ancient Greek μέλας (mélas, “black, dark”).

Related phrases

pineal gland

Data sourced from Wiktionary, WordNet, CMU, and other open linguistic databases. Updated March 2026.