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fast red

noun, often capitalized F&R

Definition of fast red

: any of several fast red azo dyes: such as
a : a monoazo acid dye that dyes wool and silk red

— called also Fast Red A

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

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