The best replacement for fool is knave.

The best alternatives to fool are rated as following:
★★★★★  knave
★★★★  idiot
★★★★  jo cool
★★★★  wise
★★★  morningstar
★★★  fool who follows the fool
★★  joe cool
★  fools
★  seeking alpha
★  let a fool kiss you
★  clown
★  fool
★  april fools
  jester
  cool
  dave ramsey
  trickster
  fool that follows the fool
  wise man

Your alternative for fool is not listed? Suggest!
Speaking about fool, one probably shouldn't forget about tool is still a fool.

Other search terms related to fool and their ratings are:
★★★★★ tool is still a fool
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Google Trends

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fool
knave
idiot