The Collaborative International Dictionary of English v.0.48:

Accumulative \Ac*cu"mu*la*tive\, a.
   Characterized by accumulation; serving to collect or amass;
   cumulative; additional. -- Ac*cu"mu*la*tive*ly, adv. --
   Ac*cu"mu*la*tive*ness, n.
   [1913 Webster]