Definition of grunts:
(n) :
A short snorting sound, often to show disapproval, or used as a reply when one is reluctant to speak.
(n) :
The snorting cry of a pig.
(n) :
(US, military slang) An infantry soldier.
(n) :
A person who does ordinary and boring work.
(n) :
Any fish of the perciform family Haemulidae.
(n) :
(slang) The amount of power of which a vehicle is capable.