The Collaborative International Dictionary of English v.0.48:

Cumulation \Cu`mu*la"tion\ (k?`m?-l?"sh?n), n. [Cf. F.
   cumulation.]
   The act of heaping together; a heap. See Accumulation.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cumulation
    n 1: a collection of objects laid on top of each other [syn:
         pile, heap, mound, agglomerate, cumulation,
         cumulus]