The Collaborative International Dictionary of English v.0.48:

Surrenderor \Sur*ren`der*or"\, n. (Law)
   One who makes a surrender, as of an estate. --Bouvier.
   [1913 Webster]

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

SURRENDEROR. One who makes a surrender; as when the tenant gives up the
estate and cancels his lease before the expiration of the term; one who
yields up a freehold estate for the purpose of conveying it.