FRET—gall, chafe, agitate, irritate, vex.
FRIENDLY—amicable, social, sociable. (Distant, reserved, cool.)
FRIGHTFUL—fearful, dreadful, dire, direful, awful, terrific, horrible, horrid.
FRIVOLOUS—trifling, trivial, petty. (Serious.)
FRUGAL—provident, economical, saving. (Wasteful, extravagant.)
FRUITFUL—fertile, prolific, productive, abundant, plentiful, plenteous. (Barren, sterile.)
FRUITLESS—vain, useless, idle, bootless, unavailing, without avail.
FRUSTRATE—defeat, foil, balk, disappoint.
FULFILL—accomplish, effect, complete.
FULLY—completely, abundantly, perfectly.