The Collaborative International Dictionary of English v.0.48:

billfold \bill"fold`\ (b[i^]l" f[=o]ld`),
   A small, thin, flat container, usually made of leather or
   imitation leather, having a pocket of a size just large
   enough to hold paper currency and folded over once to fit in
   the pocket of one's clothing; it is a type of wallet, but
   having fewer compartments than the typical wallet.
   [PJC]

WordNet (r) 3.0 (2006):

billfold
    n 1: a pocket-size case for holding papers and paper money [syn:
         wallet, billfold, notecase, pocketbook]