The Collaborative International Dictionary of English v.0.48:

Rammer \Ram"mer\ (r[a^]m"m[~e]r), n.
   One who, or that which, rams or drives. Specifically:
   (a) An instrument for driving anything with force; as, a
       rammer for driving stones or piles, or for beating the
       earth to more solidity.
   (b) A rod for forcing down the charge of a gun; a ramrod.
   (c) (Founding) An implement for pounding the sand of a mold
       to render it compact.
       [1913 Webster]

WordNet (r) 3.0 (2006):

rammer
    n 1: a tool for driving something with force