mordant

Short definition from Wiktionary

Adjective

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

Noun

1. 1
   Any substance used to facilitate the fixing of a dye to a fibre; usually a metallic compound which reacts with the dye using chelation.
2. 2
   Any corrosive substance used in etching.
3. 3
   A glutinous size used as a ground for gilding, to make the gold leaf adhere.

Verb

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