The Collaborative International Dictionary of English v.0.48:

Sortition \Sor*ti"tion\, n. [L. sortitio, from sortiri to draw
   or cast lots, fr. sors, sortis, a lot.]
   Selection or appointment by lot. [Obs.] --Bp. Hall.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sortition
    n 1: making a chance decision by using lots (straws or pebbles
         etc.) that are thrown or drawn [syn: casting lots,
         drawing lots, sortition]