Definition of "guns"

And there's still no better way to throw down the fitness gauntlet than to roll up your sleeves and unveil some powerful guns.

2005, Joe Kita, editor, Men's Health Best: Arms, page 6

I read in another magazine about a workout that can put a whole inch on your arms in just one day! Obviously that sounds awesome, because my guns are only 15 inches.

2010, Mark Alvisi (quote from a reader), "Mark of a Champion", Muscular Development 47(1): 350