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.
3. the meat of the tuna, used as food; -- also called tuna