Whip·per·in n.
  1. A huntsman who keeps the hounds from wandering, and whips them in, if necessary, to the of chase.
  2. Hence, one who enforces the discipline of a party, and urges the attendance and support of the members on all necessary occasions.
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  whipper-in
       n : huntsman's assistant in managing the hounds
       [also: whippers-in (pl)]