four-pounder
- n an artillery gun that throws a shot weighing four pounds
four-spot
- n a playing card or domino or die whose upward face shows four pips
four-stroke engine
- n an internal-combustion engine in which an explosive mixture is drawn into the cylinder on the first stroke and is compressed and ignited on the second stroke; work is done on the third stroke and the products of combustion are exhausted on the fourth stroke
four-stroke internal-combustion engine
- n an internal-combustion engine in which an explosive mixture is drawn into the cylinder on the first stroke and is compressed and ignited on the second stroke; work is done on the third stroke and the products of combustion are exhausted on the fourth stroke