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smart as a whip

Very intelligent or clever, as in Little Brian is smart as a whip; he's only three and already learning to read. This simile alludes to the sharp crack of a whip. [Mid-1900s] Also see mind like a steel trap.

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RELATED WORDS

vigorous, effective, deft, able, active, wise, ready, sharp, keen, knowing, acute, prompt, slick, adept, whiz, savvy, adroit, apt, astute, bright
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.