One who hets or heats; someone or something that makes things hot, or a device for heating.
From het (past tense of heat, or dialectal 'heat') + -er (English suffix for one who does something or something that does something). A straightforward agent noun formation.
In old dialectal English, a 'hetter' was anyone or anything that heated—you might have a 'hetter of water' (a kettle) or call a person the 'hetter of the house,' showing how flexibly English once created words for everyday functions.
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