The Collaborative International Dictionary of English v.0.48:

FNMA \FNMA\ n.
   The Federal National Mortgage Association a federally
   chartered corporation that purchases and resells mortgages.
   [acron.]

   Syn: Federal National Mortgage Association, Fannie Mae.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

FNMA
    n 1: a federally chartered corporation that purchases mortgages
         [syn: Federal National Mortgage Association, Fannie
         Mae, FNMA]