1540s, transitive, "shed in small drops;" 1560s, intransitive, "fall in very fine particles, as water from the clouds," of uncertain origin. Perhaps it is an alteration of drysning "a falling of dew" (c. 1400), from Old English -drysnian, which is related to dreosan "to fall" (see dreary). Or perhaps it is a frequentative of Middle English dresen "to fall," from Old English dreosan. Related: Drizzled; drizzling.
As a noun, "a light rain, mist," from 1550s.