The term PART OF INTERNAL COMBUSTION ENGINE can be summarized by the solution to the crossword, PISTON. A piston is a cylindrical part of an internal combustion engine that moves up and down in a cylinder, transferring force from expanding gas in the cylinder to the crankshaft via a piston rod. It is the key component of the combustion process, as it is responsible for compressing the air-fuel mixture and then igniting it.