The Collaborative International Dictionary of English v.0.48:

Avowry \A*vow"ry\, n. [OE. avouerie protection, authority, OF.
   avouerie. See Avow to declare.]
   1. An advocate; a patron; a patron saint. [Obs.]
      [1913 Webster]

            Let God alone be our avowry.          --Latimer.
      [1913 Webster]

   2. The act of the distrainer of goods, who, in an action of
      replevin, avows and justifies the taking in his own right.
      --Blackstone.
      [1913 Webster]

   Note: When an action of replevin is brought, the distrainer
         either makes avowry, that is, avours taking the
         distress in his own right, or the right of his wife,
         and states the reason if it, as for arrears of rent,
         damage done, or the like; or makes cognizance, that is,
         acknowledges the taking, but justifies in an another's
         right, as his bailiff or servant.
         [1913 Webster]

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

AVOWRY, pleading. An avowry is where the defendant in an action of replevin,
avows the taking of the distress in his own right, or in right of his wife,
and sets forth the cause of it, as for arrears of rent, damage done, or the
like. Lawes on Pl. 35 Hamm. N. P. 464; 4 Bouv. Inst. n. 3571.
     2. An avowry is sometimes said to be in the nature of an action or of.
a declaration, and privity of estate is necessary. Co. Lit. 320 a; 1 Serg. &
R. 170-1. There is no general issue upon an avowry and it cannot be
traversed cumulatively. 5 Serg. & R. 377. Alienation cannot be replied to it
without notice; for the tenure is deemed to exist for the purposes of an
avowry till notice be given of the alienation. Ham. Parties, 131-2; Ham. N.
P. 398, 426.