Source : Webster's Revised Unabridged Dictionary (1913)

Decennary \De*cen"na*ry\, n.; pl. {Decennaries}. [L. decennium a
   period of ten years; decem ten + annus a year.]
   1. A period of ten years.

   2. (O. Eng. Law) A tithing consisting of ten neighboring
      families. --Burrill.

Source : WordNet®

decennary
     n : a period of 10 years [syn: {decade}, {decennium}]