adventurer, venturer - a person who enjoys taking risks

gambler - a person who wagers money on the outcome of games or sporting events

hedger - someone who counterbalances one transaction (as a bet) against another in order to protect against loss

operator - a speculator who trades aggressively on stock or commodity markets

scalper - someone who buys something and resells it at a price far above the initial cost; "he got theater tickets through a scalper"

venture capitalist - a speculator who makes money available for innovative projects (especially in high technology)

swimmer - a trained athlete who participates in swimming meets; "he was an Olympic swimmer"

hand tool - a tool used with workers' hands

mechanical device - mechanism consisting of a device that works on mechanical principles

piston ring - seal consisting of a split metal ring that seals the gap between a piston and the cylinder wall

piston rod - connecting rod that moves or is moved by a piston

reciprocating engine - an internal-combustion engine in which the crankshaft is turned by pistons moving up and down in cylinders