Definition of neutral red in English:

neutral red


  • A dark green crystalline azine dye, C₁₅ H₁₆ N₄ ·HCl, which forms a red solution in water or alcohol and is used as an acid-base indicator and as a biological stain (especially for granules and vacuoles in cells).


Late 19th century; earliest use found in Thomas E. Thorpe (1845–1925), chemist.