Metachromatic

Part of speech: adjective

Definitions

1. Describing a tissue component that takes on a color different from the dye applied to it during staining
2. Showing metachromasia, the property by which certain tissue structures stain in a hue unlike the dye's own color
3. Of a stain or cell structure that changes color under dye, displaying a shade other than the dye's original tint

Etymology: Metachromatic is a technical coinage, not an old word. It was built in the late nineteenth century from Greek roots: "meta", meaning change, and "khrōma", meaning colour, which also gives English "chromatic" and "chrome". The pieces mean "changing colour", and the word was formed to describe a specific laboratory effect rather than something ancient writers could have named. The effect is that certain dyes, when applied to a tissue or material, stain it a colour different from the dye's own colour. Biologists and microscopists found this useful because a stain could reveal structures through the shift in hue, and cartilage and certain cell components often show it. The word is used of the dye or of the stained material, depending on context.