borrowed from Medieval Latin, "pustule, pox," going back to Late Latin, "pustule," from varius "affected by pox, leprous" (adjective derivative of varus "pimple" + Latin -ola, variant of -ula-ule after vowels — more at varix
Note:
Late Latin varius is very likely independent of classical varius "having contrasting colors, varied" (see various entry 1).
