The Collaborative International Dictionary of English v.0.48:

Jumpy \Jump"y\, a. [Compar. Jumpier; superl. Jumpiest.]
   Jumping, or inducing to jump; characterized by jumps; hence,
   extremely nervous; jittery.

   Syn: edgy, fidgety, high-strung, in suspense(predicate),
        jittery, nervous, nervy, overstrung, restive, uneasy,
        uptight.
        [Webster 1913 Suppl. WordNet 1.5]