a shaped covering for the head worn for warmth, as a fashion item, or as part of a uniform:a black straw hata woolly hat
used to refer to a particular role or occupation of someone who has more than one:wearing her scientific hat she is director of a pharmacology research group
be all hat and no cattle
US informal tend to talk boastfully without acting on one’s words:in my view, the Senators are all mouth and no action or, as we say in my part of the country, all hat and no cattle