MELATONIN Meaning of MELATONIN in English [ ˌmɛlə'təʊnɪn ]■ noun Biochemistry a hormone secreted by the pineal gland which inhibits melanin formation.Origin1950s: from Gk melas 'black' + serotonin . Concise Oxford English vocab. Сжатый оксфордский словарь английского языка. 2004