Extricate vs. Extract
Faint vs. Feint
Fair vs. Fare
Fallible vs. Fallacious
Falseness vs. Falsehood
Farther vs. Further
Faze vs. Phase
Feet vs. Feat
Fiancee vs. Fiance
Finely vs. Finally
Fined vs. Find
Flair vs. Flare
Flaunt vs. Flout
Flew vs. Flu
Floe vs. Flow
Flounder vs. Founder
Flush vs. Blush
Font vs. Fount
Foreword vs. Forward
Formally vs. Formerly