Wiktionary
trench mortar
alt. A small mortar designed to fire shells from one trench to an enemy trench. n. A small mortar designed to fire shells from one trench to an enemy trench.
WordNet
Usage examples of "trench mortar".
Ripping open its zip fasteners they pulled out an amazing variety of items, including automatic rifles, leather ammunition-carriers, two heavy machine-guns and a squat, fat-barrelled affair that looked like a cross between a trench mortar and a small howitzer.
He's been deaf, dumb and minus his hair since a Chinese trench mortar blew him forty feet through the air.