FLU - Influenza.
FOR - Because.
FUR - Hairy coat of various mammal species, especially: when fine, soft and thick.
OFF - In a direction away from the speaker or object.
FRO - From; away; back or backward. In modern English used only in the set phrase to and fro ("back and forth").
FOLK - Of or pertaining to the inhabitants of a land, their culture, tradition, or history.
FORK - A pronged tool having a long straight handle, used for digging, lifting, throwing etc.
FOUL - Covered with, or containing, extraneous matter which is injurious, noxious, offensive, or obstructive; filthy; dirty; not clean; polluted; nasty; defiled; as, a foul cloth; foul hands; a foul chimney; foul air; a ship's bottom is foul when overgrown with barnacles; a gun becomes foul from repeated firing; a well is foul with polluted water.
FOUR - A numerical value equal to 4; the number after three and before five; two plus two.
FLOUR - Powder obtained by grinding or milling cereal grains, especially wheat, and used to bake bread, cakes, and pastry.
FORKFUL - The amount that a fork will hold.