pile driver

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A machine that drives a pile by raising a weight between guideposts and dropping it on the head of the pile.
2. n. One who operates such a machine.

Century Dictionary and Cyclopedia

1. n. A workman occupied in driving piles.
2. n. A machine or contrivance, usually worked by steam, for driving piles. A common form, shown in the cut, consists of a large ram or block of iron. which slides between two guide-posts. Being drawn up to the top, and then let fall from a considerable height, it comes down on the head of the pile with a violent blow.

Wiktionary

1. n. A machine for forcing a pile, a long beam, into the ground as part of the construction of a foundation; usually by raising a weight and then dropping it on the beam.
2. n. A person who hits or attacks forcefully or powerfully.
3. adj. forceful

GNU Webster's 1913

1. n. an apparatus for driving down piles, consisting usually of a high frame, with suitable appliances for raising to a height (by animal or steam power, the explosion of gunpowder, etc.) a heavy mass of iron, which falls upon the pile.

WordNet 3.0

1. n. a machine that drives piling into the ground