Plural form of what. Used as a stand-in to collectively pluralize arbitrary instances of things. Often used along with whys, hows, etc

Plural form of that

A protective head covering made of hard material, such as leather, metal, or plastic, The headgear with a glass mask worn by deep-sea divers, A hat of similar form worn by policemen, or by civilians for any purpose, especially in not climates Such hats are usually of felt or pith, so formed as to have space for ventilation around the head or openings for ventilation above

Plural form of hat