Counterstains

Part of speech: noun

Definitions

1. A dye or colorant applied to a specimen to provide contrast against another stain in microscopy
2. A secondary staining process used to enhance visibility of certain structures in biological samples
3. An additional layer of color used to improve the differentiation of various components in histological analysis

Etymology: "Counterstains" is the plural of "counterstain," a compound of "counter-" and "stain." The first element comes from Latin "contrā," meaning "against" or "opposite," which passed through Old French "contre" and Anglo-Norman "countre" before reaching Middle English as "counter-." The second element, "stain," is English, so the whole word is a plain English formation: a stain that works against another stain. The logic of the compound fits the laboratory practice it names. In microscopy, a specimen is often treated with one dye to colour a structure, and a second dye is then applied so that surrounding tissue or other features stand out in a different hue. The second dye is set against the first, which is exactly what "counter-" signals. The word is a technical formation built from ordinary English parts rather than an older term carried over into science.