The Collaborative International Dictionary of English v.0.48:

Bonito \Bo*ni"to\ (b[-o]*n[=e]"t[-o]), n.; pl. Bonitoes
   (-t[-o]z). [Sp. & Pg. bonito, fr. Ar. bain[imac]t and
   bain[imac]th.] [Often incorrectly written bonita.] (Zool.)
   1. A large tropical fish (Orcynus pelamys) allied to the
      tunny. It is about three feet long, blue above, with four
      brown stripes on the sides. It is sometimes found on the
      American coast.
      [1913 Webster]

   2. any of a variety of scombroid fishes of the genera Sarda
      or Euthynnus, with a size intermediate between those of
      the smaller mackerels and the tunas. It is applied
      especially to the skipjack tuna (Euthynnus pelamis,
      syn. Katsuwonus pelamis, formerly Sarda Mediterranea,
      also called skipjack) of the Atlantic, an important and
      abundant food fish on the coast of the United States, and
      (Sarda Chilensis) of the Pacific, and other related
      species. These are large and active fishes, of a blue
      color above and silver below, with black oblique stripes.
      --MW10
      [1913 Webster +PJC]

   3. The medregal (Seriola fasciata), an edible fish of the
      southern part of the United States and the West Indies.
      [1913 Webster]

   4. The cobia or crab eater (Elacate canada), an edible fish
      of the Middle and Southern United States.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cobia \Co"bi*a\, n. (Zool.)
   An oceanic fish of large size (Elacate canada); the
   crabeater; -- called also bonito, cubbyyew, coalfish,
   and sergeant fish.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bonito
    n 1: flesh of mostly Pacific food fishes of the genus Sarda of
         the family Scombridae; related to but smaller than tuna
    2: fish whose flesh is dried and flaked for Japanese cookery;
       may be same species as skipjack tuna [syn: bonito, oceanic
       bonito, Katsuwonus pelamis]
    3: any of various scombroid fishes intermediate in size and
       characteristics between mackerels and tunas