The Collaborative International Dictionary of English v.0.48:

Poursuivant \Pour"sui*vant\, n.
   See Pursuivant.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Pursuivant \Pur"sui*vant\, n. [F. poursuivant, fr. poursuivre.
   See Pursue, and cf. Pursuant.] [Written also
   poursuivant.]
   1. (Heralds' College) A functionary of lower rank than a
      herald, but discharging similar duties; -- called also
      pursuivant at arms; an attendant of the heralds. Also
      used figuratively.
      [1913 Webster]

            The herald Hope, forerunning Fear,
            And Fear, the pursuivant of Hope.     --Longfellow.
      [1913 Webster]

   2. The king's messenger; a state messenger.
      [1913 Webster]

            One pursuivant who attempted to execute a warrant
            there was murdered.                   --Macaulay.
      [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

POURSUIVANT. A follower, a pursuer. In the ancient English law, it signified
an officer who attended upon the king in his wars, at the council table,
exchequer, in his court, &e., to be sent as a messenger. A poursuivant was,
therefore, a messenger of the king.