Source : Webster's Revised Unabridged Dictionary (1913)

Assignor \As`sign*or"\, n. [L. assignator. Cf. {Assigner}.]
   (Law)
   An assigner; a person who assigns or transfers an interest;
   as, the assignor of a debt or other chose in action.

Source : WordNet®

assignor
     n : (law) the party who makes an assignment