Source : Webster's Revised Unabridged Dictionary (1913)

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].

Source : WordNet®

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