piston

What it means

1. engineeringA solid disk or cylinder that fits inside a hollow cylinder, and moves under pressure (as in an engine) or displaces fluid (as in a pump)
2. entertainmentA valve device in some brass instruments for changing the pitch

In a sentence

The Latino warrior fucked like a man possessed. His lean hips powered the pistoning rod in short, vicious jabs, so rapidly that the shit-streaked cock was a blur as it pounded Captain Randall's butthole, churning the screaming soldier's ass-juices, rectal blood, and smashed turds into a slimy froth.

1991, Etienne, “In Enemy Hands”, in Drummer, number 151, page 32

Where it comes from

1. Frenchpiston
2. Frenchpiston
3. Englishpiston

Borrowed from French piston.