indigotinPronunciation: /ɪnˈdɪgətɪn, ˌɪndɪˈgəʊtɪn/Definition of indigotin noun [mass noun] Chemistry a dark blue crystalline compound which is the main constituent of the dye indigo. Chemical formula: (C8H6N0)2 Origin: mid 19th century: from indigo + -t- (for ease of pronunciation) + -in1indigotin in other Oxford dictionaries Definition of indigotin in the US English dictionary