fidejussor

from The Collaborative International Dictionary of English v.0.48

Fidejussor \Fi`de*jus"sor\, n. [L.: cf. F. fid['e]jusseur.]
   (Civil Law)
   A surety; one bound for another, conjointly with him; a
   guarantor. --Blackstone.
   [1913 Webster]

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

FIDE-JUSSOR, civil law. One who becomes security for the debt of another, 
promising to pay it in case the principal does not do so. 
     2. He differs from co-obligor in this, that the latter is equally bound 
to a debtor with his principal, while the former is not liable till the 
principal has failed to fulfill his engagement. Dig. 12, 4, 4; Id. 16, 1, 13;

Id. 24, 3, 64; Id. 38, 1, 37; Id. 50, 17, 110, and 14, 6, 20; Hall's Pr. 33; 
Dunl. Ad. Pr. 300; Clarke's Prax. tit. 63, 4, 5. 
     3. The obligation of the fide-jussor was an accessory contract, for, if 
the principal obligation was not previously contracted, his engagement then 
took the name of mandate. Lec. Elem. Sec. 872; Code Nap. 2012.