noun
Usage: often capitalized F&R
: any of several fast red azo dyes: as
a. : a monoazo acid dye that dyes wool and silk red — called also Fast Red A ; see dye table I (under Acid Red 88 )
b. : a monoazo acid dye that dyes wool and silk claret and is used chiefly as a biological stain — called also Bordeaux B, Bordeaux red, Fast Red B ; see dye table I (under Acid Red 17 )