The Collaborative International Dictionary of English v.0.48:

Demandant \De*mand"ant\n. [F. demandant, p. pr. of demander.]
   One who demands; the plaintiff in a real action; any
   plaintiff.
   [1913 Webster]

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

DEMANDANT, practice. The plaintiff or party who brings a real action, is
called the demandant. Co. Litt. 127; 1 Com. Dig. 85.