startle (v.)

c. 1300, " move agitatedly, run to and fro" (intransitive), also "caper, romp, skip; leap, jump;" from Old English steartlian, from the source of start (v.) + frequentative suffix -le (as in topple, jostle, fizzle, etc. Sense of "move suddenly in surprise or fear" first recorded 1520s. Transitive meaning "frighten suddenly" is from 1590s. The word retains more of the original meaning of start (v.). Related: Startled; startling; startlingly. As a noun from 1714.