Source : Webster's Revised Unabridged Dictionary (1913)

High-strung \High"-strung`\, a.
   Strung to a high pitch; spirited; sensitive; as, a
   high-strung horse.

Source : WordNet®

high-strung
     adj : being in a tense state [syn: {edgy}, {highly strung}, {in
           suspense(p)}, {jittery}, {jumpy}, {nervy}, {overstrung},
            {restive}, {uptight}]