“fast blue”

We have one entry that includes the term fast blue.

wool fast blue

noun, often capitalized W&F&B

: any of several blue azine acid dyes

See the full definition

Word of the Day

Listen to the pronunciation of cachet

See Definitions and Examples »

Test Your Vocabulary

Face Your Fears

  • clown-mask
  • Arachnophobia is the fear of what multi-legged creatures?
Name That Thing

You know what it looks like… but what is it called?

TAKE THE QUIZ
Play Blossom: Solve today's spelling word game by finding as many words as you can using just 7 letters. Longer words score more points.

Pick the best words!

PLAY
Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

Games & Quizzes

See All
Play Quordle: Guess all four words in a limited number of tries. Each of your guesses must be a real 5-letter word.
Quordle Can you solve 4 words at once?
Play Blossom: Solve today's spelling word game by finding as many words as you can using just 7 letters. Longer words score more points.
Blossom Word Game Pick the best words!
Play Missing Letter: a crossword with a twist. Each of the 25 puzzle words start with a different letter of the alphabet. Which letter is missing?
Missing Letter A daily crossword with a twist
silhouette of a man with a megaphone against a british flag
Another Great British Vocabulary Quiz, Innit? A double-decker quiz with words from across the pond