The Collaborative International Dictionary of English v.0.48:

Lake \Lake\, n. [AS. lac, L. lacus; akin to AS. lagu lake, sea,
   Icel. l["o]gr; OIr. loch; cf. Gr. la`kkos pond, tank. Cf.
   Loch, Lough.]
   A large body of water contained in a depression of the
   earth's surface, and supplied from the drainage of a more or
   less extended area.
   [1913 Webster]

   Note: Lakes are for the most part of fresh water; the salt
         lakes, like the Great Salt Lake of Utah, have usually
         no outlet to the ocean.
         [1913 Webster]

   Lake dwellers (Ethnol.), people of a prehistoric race, or
      races, which inhabited different parts of Europe. Their
      dwellings were built on piles in lakes, a short distance
      from the shore. Their relics are common in the lakes of
      Switzerland.

   Lake dwellings (Archaeol.), dwellings built over a lake,
      sometimes on piles, and sometimes on rude foundations kept
      in place by piles; specifically, such dwellings of
      prehistoric times. Lake dwellings are still used by many
      savage tribes. Called also lacustrine dwellings. See
      Crannog.

   Lake fly (Zool.), any one of numerous species of dipterous
      flies of the genus Chironomus. In form they resemble
      mosquitoes, but they do not bite. The larvae live in
      lakes.

   Lake herring (Zool.), the cisco (Coregonus Artedii).

   Lake poets, Lake school, a collective name originally
      applied in contempt, but now in honor, to Southey,
      Coleridge, and Wordsworth, who lived in the lake country
      of Cumberland, England, Lamb and a few others were classed
      with these by hostile critics. Called also lakers and
      lakists.

   Lake sturgeon (Zool.), a sturgeon (Acipenser rubicundus),
      of moderate size, found in the Great Lakes and the
      Mississippi River. It is used as food.

   Lake trout (Zool.), any one of several species of trout and
      salmon; in Europe, esp. Salmo fario; in the United
      States, esp. Salvelinus namaycush of the Great Lakes,
      and of various lakes in New York, Eastern Maine, and
      Canada. A large variety of brook trout (Salvelinus
      fontinalis), inhabiting many lakes in New England, is
      also called lake trout. See Namaycush.

   Lake whitefish. (Zool.) See Whitefish.

   Lake whiting (Zool.), an American whitefish (Coregonus
      Labradoricus), found in many lakes in the Northern United
      States and Canada. It is more slender than the common
      whitefish.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Namaycush \Nam"ay*cush\, n. [Indian name.] (Zool.)
   A large North American lake trout (Salvelinus namaycush).
   It is usually spotted with red, and sometimes weighs over
   forty pounds. Called also Mackinaw trout, lake trout,
   lake salmon, salmon trout, togue, and tuladi.
   [1913 Webster]

WordNet (r) 3.0 (2006):

lake trout
    n 1: flesh of large trout of northern lakes
    2: large fork-tailed trout of lakes of Canada and the northern
       United States [syn: lake trout, salmon trout, Salvelinus
       namaycush]