Resistance is futile:
hat ( P ) Pronunciation Key (ht)
n.
A covering for the head, especially one with a shaped crown and brim.
A head covering of distinctive color and shape worn as a symbol of office.
The office symbolized by the wearing of such a head covering.
A role or office symbolized by or as if by the wearing of different hats: wears two hatsone as parent and one as corporate executive.
vi·sor also vi·zor ( P ) Pronunciation Key (vzr)
n.
A piece projecting from the front of a cap or an elastic headband to shade or protect the eyes.
A fixed or movable shield against glare attached above the windshield of an automotive vehicle.
The front piece of the helmet of a suit of armor, capable of being raised and lowered and designed to protect the eyes, nose, and forehead.
A means of concealment or disguise; a mask.
There is a difference. A hat covers the head and can even have a visor. So a visor is just for shade, while a hat is for covering.
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The Rhymin' Red Rover, that's what they call me,
Too old for a sailin', too young fo' the sea;
Set sail fo' a sunset, to a land that is free,
I'm the Rhymin' Red Rover, and that's where I'll be.