startle

Short definition from Wiktionary

Verb

1. 1
   To move suddenly, or be excited, on feeling alarm; to start.
2. 2
   To excite by sudden alarm, surprise, or apprehension; to frighten suddenly and not seriously; to alarm; to surprise.
3. 3
   To deter; to cause to deviate.

Noun

1. 1
   A sudden motion or shock caused by an unexpected alarm, surprise, or apprehension of danger.