PROPOSITUS

from WordNet (r) 3.0 (2006)
propositus
    n 1: the person immediately affected by or concerned with an
         action
    
from Bouvier's Law Dictionary, Revised 6th Ed (1856)
PROPOSITUS. The person proposed. In making genealogical tables, the person 
whose relations it is desirous to find out, is called the propositus. 
    

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