Nickname for a large VERY heavily muscled man, more likely a powerlifter or strongman than a bodybuilder. Usually used when the guy looks the part-- sweat-soaked T-shirt, lifting belt, chalk dust, etc. Calling a woman strength athlete "Gruntus" is usually an insult, so choose wisely.
GymRat: "I'm gonna do some deadlifts, got any chalk?"
Lifter: "Naah, go ask Gruntus over at the power rack."
GymRat: "No way, man, he looks like he'd snap me like a toothpick!"