The Collaborative International Dictionary of English v.0.48:

Decad \Dec"ad\, n.
   A decade.
   [1913 Webster]

         Averill was a decad and a half his elder. --Tennyson.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Decade \Dec"ade\, n. [F. d['e]cade, L. decas, -adis, fr. Gr. ?,
   fr. de`ka ten. See Ten.]
   A group or division of ten; esp., a period of ten years; a
   decennium; as, a decade of years or days; a decade of
   soldiers; the second decade of Livy. [Written also decad.]
   [1913 Webster]

         During this notable decade of years.     --Gladstone.
   Decadence