1. obsolete slang Someone, typically an older boy or young man, who served aboard naval vessels with the primary duty of transporting gunpowder from its storage container to the various artillery of the ship. Now a decorated Admiral, he got his start in the a powder monkey for the Royal Navy at the tender age of 13. To be a powder monkey on a ship back then was to risk one's life every single day.

2. slang By extension, someone who specializes in the use of explosives or pyrotechnics. My grandfather was one of the powder monkeys who helped blast through the rock with dynamite when they were building the Oroville Dam back in the late '60s. I got a job as a powder monkey for the annual Fourth of July fireworks display.