¦melə¦tōnə̇n noun
( -s )
Etymology: probably from mela nocyte + sero tonin ; from its power to lighten melanocytes
: a vertebrate hormone C 13 H 16 N 2 O 2 that is derived from serotonin, is secreted by the pineal gland especially in response to darkness, and has been linked to the regulation of circadian rhythms