The Collaborative International Dictionary of English v.0.48:

Brazil nut \Bra*zil" nut`\ (br[.a]*z[i^]l" n[u^]t`). (Bot.)
   An oily, three-sided nut, the seed of the Bertholletia
   excelsa; the cream nut.
   [1913 Webster]

   Note: From eighteen to twenty-four of the seeds or "nuts"
         grow in a hard and nearly globular shell.
         [1913 Webster] Brazil wood

WordNet (r) 3.0 (2006):

brazil nut
    n 1: tall South American tree bearing brazil nuts [syn: brazil
         nut, brazil-nut tree, Bertholletia excelsa]
    2: three-sided tropical American nut with white oily meat and
       hard brown shell [syn: brazil nut, brazil]