(transitive) To heat something after it has cooled off, especially previously cooked food (also in figurative senses).
I’m reheating some leftovers for dinner.
1649, uncredited translator, A Discourse of a Method for the Well Guiding of Reason, and the Discovery of Truth in the Sciences by René Descartes, London, Part 5, p. 85,
And if we examine how this heat is communicated to the other members, must we not avow that ’tis by means of the bloud, which passing the heart, reheats it self there, and thence disperseth it self thorow the whole body:
(intransitive) To become hot again after having cooled off (also in figurative senses).
He put the soup on the stove to reheat.
2011 Helen Hollick, I am the Chosen King [UK title: Harold the King], Naperville, IL: Sourcebooks, Part 3, Chapter 7, p. 416,
Dissension was reheating in southern Wales, but at least Wales could be quashed.