The Collaborative International Dictionary of English v.0.48:

Amassment \A*mass"ment\, n. [Cf. OF. amassement.]
   An amassing; a heap collected; a large quantity or number
   brought together; an accumulation.
   [1913 Webster]

         An amassment of imaginary conceptions.   --Glanvill.
   [1913 Webster]