Source : Webster's Revised Unabridged Dictionary (1913)

Jounce \Jounce\, v. t. & i. [imp. & p. p. {Jounced}; p. pr. &
   vb. n. {Jouncing}.] [Cf. {Jaunce}.]
   To jolt; to shake, especially by rough riding or by driving
   over obstructions.

Jounce \Jounce\, n.
   A jolt; a shake; a hard trot.

Source : WordNet®

jounce
     n : a sudden impact; "the door closed with a jolt" [syn: {jolt},
          {jar}]
     v : move up and down repeatedly [syn: {bounce}]