from
The Collaborative International Dictionary of English v.0.48
Grunt \Grunt\ (gr[u^]nt), n.
1. A deep, guttural sound, as of a hog.
[1913 Webster]
2. (Zool.) Any one of several species of American food
fishes, of the genus {Haemulon}, allied to the snappers,
as, the black grunt ({Haemulon Plumieri}), and the
redmouth grunt ({Haemulon aurolineatus}), of the Southern
United States; -- also applied to allied species of the
genera {Pomadasys}, {Orthopristis}, and {Pristopoma}.
Called also {pigfish}, {squirrel fish}, and {grunter}; --
so called from the noise it makes when taken.
[1913 Webster]
3. A U. S. infantryman; -- used especially of those fighting
in the war in Vietnam. [slang]
[PJC]