acid-fast

adjective ac·id-fast \ ˈa-səd-ˌfast \

Definition of acid-fast

: not easily decolorized by acids

First Known Use of acid-fast

1903

in the meaning defined above

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Medical Dictionary

acid-fast

adjective \ ˈas-əd-ˌfast \

medical Definition of acid-fast

: not easily decolorized by acids (as when stained) used especially of bacteria and tissues

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