The Collaborative International Dictionary of English v.0.48:

Recognizor \Re*cog`ni*zor"\ (r[-e]*k[o^]g`n[i^]*z[^o]r" or
   r[-e]*k[o^]n`[i^]*z[^o]r"), n. (Law)
   One who enters into a recognizance. [Written also
   recognisor.] --Blackstone.
   [1913 Webster]

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

RECOGNISOR, contracts. He who enters into a recognizance.