Definitions for vat dye
Random House Webster's College Dictionary
any of a class of water-insoluble dyes that are taken up by textile fibers and then fixed by oxidation.
Origin of vat dye:
vat dye, vat color(noun)
a water-insoluble dye that is applied by reducing the dye to an alkaline form, applying the dye, then regenerating the insoluble dye by oxidation in the material; used for dyeing cotton
Any of a type of dye, many based on indigo, in which a soluble form is used to impregnate a fibre or fabric and is then converted to an insoluble form