[1] : The Collaborative International Dictionary of English v.0.48

tuna \tu"na\, n. cf. tunny.
   1. zool. any one of several species of large oceanic fishes
      belonging to the mackerel family scombridae, especially
      the bluefin tuna thunnus thynnus, formerly orcynus
      thynnus or albacora thynnus, called also the common
      tunny or great tunny, a native of the mediterranean sea
      and of temperate parts of the atlantic ocean. it sometimes
      weighs a thousand pounds or more, and is caught
      commercially in large quantity for use as food; -- also
      called, especially in britain, tunny. it is also one of
      the favorite fishes used by the japanese in preparing
      sushi. on the american coast, especially in new england,
      it is sometimes called the horse mackerel. another
      well-known species is the yellowfin tuna thunnus
      albacares of warm seas. the see illust. of horse
      mackerel, under horse.

   note: the little tunny gymnosarda alletterata of the
         mediterranean and north atlantic, and the long-finned
         tunny, or albacore thunnus alalunga see
         albacore, are related species of smaller size.
         1913 webster +pjc

   2. the bonito, 2.
      1913 webster

   3. the meat of the tuna, used as food; -- also called tuna
      fish.
      pjc
see also:
tunny scombridae bluefin tuna thunnus thynnus orcynus thynnus albacora thynnus 
common tunny great tunny tunny horse mackerel yellowfin tuna 
thunnus albacares horse mackerel horse gymnosarda alletterata thunnus alalunga 
albacore tuna fish 

[2] : WordNet (r) 2.0

bluefin tuna
     n 1: flesh of very large tuna syn: bluefin
     2: largest tuna; to 1500 pounds; of mostly temperate seas: feed
        in polar regions but breed in tropics syn: bluefin, horse
        mackerel, thunnus thynnus
see also:
bluefin horse mackerel thunnus thynnus 

Tuna >> T Words
Tuna, definition of term: Tuna
tuna_pag1.html

Bluefin >> B Words
Bluefin, definition of term: Bluefin
bluefin_pag1.html

Tuna Fish >> T Words
Tuna Fish, definition of term: Tuna Fish
tuna+fish_pag1.html

Skipjack Tuna >> S Words
Skipjack Tuna, definition of term: Skipjack Tuna
skipjack+tuna_pag1.html