mordant

adj

1. Having or showing a sharp or critical quality.
2. Serving to fix a dye to a fiber.

noun

1. (countable, uncountable)Any substance used to facilitate the fixing of a dye to a fibre; usually a metallic compound which reacts with the dye using chelation.

   “In dyeing two mediums are required, the colouring matter and the mordant which fixes the dye in the wool.”

2. (countable, uncountable)Any corrosive substance used in etching.
3. (countable, uncountable)A glutinous size used as a ground for gilding, to make the gold leaf adhere.

verb

1. (transitive)To subject to the action of, or imbue with, a mordant.

   “Mordant these goods for dyeing.”