small mortar for throwing grenades
• (n.) A small bronze mortar mounted on a wooden block with handles, and light enough to be carried short distances by two men.
Coe'horn noun [ From its inventor, Baron Coehorn .] (Mil.) A small bronze mortar mounted on a wooden block with handles, and light enough to be carried short distances by two men. 
A coehorn was a small howitzer of about 4.5 inches calibre. They were named after Baron von Coehorn of Holland.