|thī(ˌ)ō+ noun
Etymology: International Scientific Vocabulary thi- + indigo
1. : a red vat dye C 16 H 8 O 2 S 2 like indigo in chemical structure except for replacement of both imino groups by sulfur atoms — see dye table I (under Vat Red 41 )
2. : any of several vat dyes derived from or closely related to thioindigo — see dye table I