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]

WordNet (r) 3.0 (2006):

jumpy
    adj 1: being in a tense state [syn: edgy, high-strung,
           highly strung, jittery, jumpy, nervy,
           overstrung, restive, uptight]
    2: causing or characterized by jolts and irregular movements; "a
       rough ride" [syn: rough, rocky, bumpy, jolty,
       jolting, jumpy] [ant: smooth]