c. 1300, "run to and fro" (intransitive), frequentative of sterten (see start (v.)). 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.
