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