noun (n)

• a rapid, jerky movement of the eyes between positions of rest(noun.act)

  source: wordnet30
• an abrupt spasmodic movement(noun.act)

  Synonym:
  jerk, jerking, jolt
  

  source: wordnet30
• A sudden, violent check of a horse by drawing or twitching the reins on a sudden and with one pull.(noun)

  source: webster1913