Fealins, failings.
Fecket, an undershirt or waistcoat made of flannel or worsted.
Feckless, weak, poor-spirited.
Feif-titty, thief-sister.
Feike, screw, force.
Fey, try.
Fied, feed, engaged.
Figs, a petty oath.
Fint, feint, an interjection probably derived from the word ‘fiend.’
Flighter, an unsteady, high-flown person.