Webster's Revised Unabridged Dictionary · 1913

Grunt

Grunt (grunt) , transitive verb

[Old English grunten; akin to As. grunian, German grunzen, Danish grynte, Swedish grymta; all prob. of imitative; or perh. akin to English groan.]

To make a deep, short noise, as a hog; to utter a short groan or a deep guttural sound.
Who would fardels bear, To grunt and sweat under a weary life. — Shakespeare
Collocations (1)
Grunting ox (Zoology) , the yak.

Grunt (grunt) , noun

1.
A deep, guttural sound, as of a hog.
2.
(Zoology) 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.
3.
A U. S. infantryman; -- used especially of those fighting in the war in Vietnam. [slang]