feasible
workable; plausible; possible
Homer’s idea of opening a hair salon for bald people was not feasible—who
would pay the $30 fee? D’oh!
fervor
passion
I will fight a ferocious ferret and get its fur for you if it will prove the fervor of
my love for you.
fictitious
false; not genuine
Books of fiction have fictitious plots.
fluctuation
irregular variation