The Collaborative International Dictionary of English v.0.48:

blowfish \blow"fish\ n.
   1. a fish eaten as a delicacy, especially in Japan. It is
      highly dangerous because of a potent nerve poison
      (tetrodotoxin) in its ovaries and liver. Chefs require
      special training to learn how to remove the poisonous
      parts, and in Japan they must be licensed.

   Note: In Japan it is called fugu. Deaths due to ingestion
         of the meat of this fish occur almost every year.

   Syn: sea squab, puffer, puffer fish.
        [WordNet 1.5 +PJC]

   2. any of numerous marine fishes of the family
      Tetraodontidae whose elongated spiny body can inflate
      itself with water or air to form a globe; several species
      contain tetrodotoxin, a potent nerve poison; they are
      closely related to spiny puffers.

   Syn: puffer, globefish.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

blowfish
    n 1: delicacy that is highly dangerous because of a potent nerve
         poison in ovaries and liver [syn: blowfish, sea squab,
         puffer, pufferfish]
    2: any of numerous marine fishes whose elongated spiny body can
       inflate itself with water or air to form a globe; several
       species contain a potent nerve poison; closely related to
       spiny puffers [syn: puffer, pufferfish, blowfish,
       globefish]