• synonyms


[as-id-fast, -fahst]
  1. resistant to decolorizing by acidified alcohol after staining.
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Origin of acid-fast

First recorded in 1900–05
Related formsac·id-fast·ness, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for acid-fast

Historical Examples

  • The acid-fast bacteria are particularly rich in fatty substances, especially the higher wax-like fats.

    The Fundamentals of Bacteriology

    Charles Bradfield Morrey

  • Other bacteria than the acid-fast group are stained blue by Gabbet's method.

  • This method is supposed to differentiate between B. tuberculosis and other acid-fast micro-organisms.

British Dictionary definitions for acid-fast


  1. (of bacteria and tissues) resistant to decolorization by mineral acids after staining
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Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

acid-fast in Medicine


  1. Of or relating to bacteria that are not decolorized by an acidic alcohol solution after they have been stained.
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Related formsacid-fast′ness n.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.