The Collaborative International Dictionary of English v.0.48:

Accelerative \Ac*cel"er*a*tive\, a.
   Relating to acceleration; adding to velocity; quickening.
   --Reid.
   [1913 Webster]

WordNet (r) 3.0 (2006):

accelerative
    adj 1: tending to increase velocity [syn: accelerative,
           acceleratory]