The Collaborative International Dictionary of English v.0.48:

Decil \Dec"il\, Decile \Dec"ile\, n. [F. d['e]cil, fr. L. decem
   ten? cf. It. decile.] (Astrol.)
   An aspect or position of two planets, when they are distant
   from each other a tenth part of the zodiac, or 36[deg].
   [1913 Webster] Deciliter

WordNet (r) 3.0 (2006):

decile
    n 1: (statistics) any of nine points that divided a distribution
         of ranked scores into equal intervals where each interval
         contains one-tenth of the scores