The Collaborative International Dictionary of English v.0.48:

halfpenny \half"pen*ny\, half-penny
\half"-pen*ny\(h[=a]"p[e^]n*n[y^] or h[aum]f"-; 277), n.;pl.
   Half-pence (-pens) or Half-pennies(-p[e^]n*n[i^]z).
   An English coin of the value of half a penny, no longer
   minted; also, the value of half a penny.

   Syn: ha'penny.
        [1913 Webster + WordNet 1.5]

WordNet (r) 3.0 (2006):

halfpenny
    n 1: an English coin worth half a penny [syn: halfpenny,
         ha'penny]