People who operate cremation equipment, or the machines/furnaces themselves that burn bodies to ash.
Agent noun from cremate (to reduce to ashes by burning), with the -or suffix indicating a person who performs an action or a device that performs it. Cremate derives from Latin cremare (to burn).
Cremators as a profession emerged in the late 1800s, and the word shows how English flexibly uses the -or suffix for both people and machines—like how a 'generator' both names the machine and describes what it does.
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