1670s, "a drawing on strong paper" (used as a model for another work), from French carton or directly from Italian cartone "strong, heavy paper, pasteboard," thus "preliminary sketches made by artists on such paper" (see carton). Extension to drawings in newspapers and magazines is by 1843. Originally they were to advocate or attack a political faction or idea; later they were merely comical as well.
Punch has the benevolence to announce, that in an early number of his ensuing Volume he will astonish the Parliamentary Committee by the publication of several exquisite designs, to be called Punch's Cartoons! ["Punch," June 24, 1843]
Also see -oon. As "an animated movie," by 1916.