Question

a big fish in a small pond
 a big fish in a small pond  (chiefly US)   ( or Brit   a big fish in a little pond)
  : a person who is very well known or important in a small group of people but who is not known or important outside that group
   In school he was a big fish in a small pond, but once he moved to the city he was just another struggling actor.
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 Main Entry: fish
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 a big fish in a small pond — see fish, 1
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 Main Entry: pond
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 a big fish in a small pond — see fish, 1
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 Main Entry: small