The Collaborative International Dictionary of English v.0.48:

GATT \GATT\ prop. n. [General Agreement on Tarriffs and Trade.]
   a United Nations agency created by a multinational treaty to
   promote trade by the reduction of tariffs and import quotas.
   [acronym]

   Syn: General Agreement on Tarriffs and Trade.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

GATT
    n 1: a United Nations agency created by a multinational treaty
         to promote trade by the reduction of tariffs and import
         quotas [syn: General Agreement on Tariffs and Trade,
         GATT]