cautioner

from The Collaborative International Dictionary of English v.0.48

Cautioner \Cau"tion*er\, n.
   1. One who cautions or advises.
      [1913 Webster]

   2. (Scots Law) A surety or sponsor.
      [1913 Webster]

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

CAUTIONER, Scotch law, contracts. One who becomes bound as caution or surety 
for another, for the performance of any obligation or contract contained in 
a deed.

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