Old English flicorian "to flutter, flap quickly and lightly, move the wings," originally of birds. Onomatopoeic and suggestive of quick motion. Sense of "shine with a wavering light" is c. 1600, but not common till 19c. Related: Flickered; flickering.
type of North American woodpecker, 1808, American English, said to be echoic of bird's note, or from black spots on plumage of the underparts that seem to flicker as it flits from tree to tree.