• Once bitten, twice shy.
  • One father is (worth) more than a hundred schoolmasters.
  • One good turn deserves another.
  • One of these days is none of these days.
  • One today is worth two tomorrows.
  • One man’s meat is another man’s poison.
  • One man’s trash is another man’s treasure.
  • Opportunity seldom knocks twice.
  • Out of the mouth of babes and sucklings.