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
Test Your Vocabulary
Who Knew?
-
- What is a ruelle?

Test your visual vocabulary with our 10-question challenge!
TAKE THE QUIZ
Anagram puzzles meet word search.
TAKE THE QUIZLove words? Need even more definitions?
Merriam-Webster unabridged
Words at Play
Ask the Editors
Share fast red