serotonin serotinous • serotoxin · · · Info · Definitions · Synonyms · Characters · · serotonin · · Text Latin · · Script 9 · · Length 4 · · Syllables Definitions · · · (noun) a neurotransmitter involved in e.g. sleep and depression and memory. Synonyms: 5-hydroxytryptamine. · · Noun Definition 1 Synonyms · · · 5-hydroxytryptamine · · Synonym 1 Characters · · e latin small letter e U+0065 i latin small letter i U+0069 n latin small letter n U+006E o latin small letter o U+006F r latin small letter r U+0072 s latin small letter s U+0073 t latin small letter t U+0074