1. Impossible to achieve
   - unachievable, unattainable, undoable, unrealizable

See also: impossible

• F layer
• f number
• F region
• f-word
• F. D. Roosevelt
• F. G. Banting
• F. Scott Fitzgerald
• fa
• fa la
• FAA
• fab
• Fabaceae
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• fabian
• Fabian Society
• Fabiana
• Fabiana imbricata
• Fabianism
• fable
• fabled
• fabler
• fabliau
• fabric
• fabricate
• fabricated