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]

Moby Thesaurus II by Grady Ward, 1.0:

93 Moby Thesaurus words for "jumpy":
   agitated, all shook up, all-overish, anxious, bashful, bustling,
   convulsive, cowardly, diffident, discomposed, disquieted,
   disturbed, eclamptic, edgy, excited, fearful, fearing, fearsome,
   feverish, fidgeting, fidgety, fitful, flurried, flustered,
   fluttering, fluttery, fretful, fussing, fussy, goosey, goosy,
   high-strung, in a quiver, in fear, jerking, jerky, jiggety,
   jittery, mousy, nervous, nervy, on edge, orgasmic, panicky,
   perturbed, queasy, quivering, quivery, rabbity, restive, restless,
   ruffled, saltatory, scary, shaken, shaken up, shaking, shaky,
   shivering, shivery, shook up, shrinking, shy, skittery, skittish,
   spasmodic, spastic, spooky, startlish, stirred up, tense, timid,
   timorous, trembling, trembly, tremulant, tremulous, trepidant,
   trigger-happy, troubled, troublous, turbulent, twitchety,
   twitching, twitchy, twittery, uneasy, unpeaceful, unquiet,
   unrestful, unsettled, upset, vellicative