The Collaborative International Dictionary of English v.0.48:

Avowant \A*vow"ant\, n. (Law)
   The defendant in replevin, who avows the distress of the
   goods, and justifies the taking. --Cowell.
   [1913 Webster]

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

AVOWANT, practice, pleading. One who makes an avowry.