from The American Heritage® Dictionary of the English Language, 5th Edition.
- noun An early, crudely made musket.
- noun A long heavy cannon used in the 16th and 17th centuries.
from The Century Dictionary.
- noun An early name of the cannon.
from the GNU version of the Collaborative International Dictionary of English.
- noun A long cannon of the 16th century, usually an 18-pounder with serpent-shaped handles.
from Wiktionary, Creative Commons Attribution/Share-Alike License.
- noun A kind of
- noun A large
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- noun a heavy cannon with a long barrel used in the 16th and 17th centuries
- noun a medieval musket
from The American Heritage® Dictionary of the English Language, 4th Edition
from Wiktionary, Creative Commons Attribution/Share-Alike License
Culverin: The culverin is a medium cannon firing an 18 lb shot.
French had just succeeded in taking across the last piece of artillery, a long "culverin"  (cannon), named _Madame de Forli_,  which had been re-taken from the Spaniards at Ravenna, was so heavy that it sank the first boat, and the poor soldiers, seeing they were lost, escaped as best they could, but many were killed and others drowned.
Like many gun names, the word "culverin" has a metaphorical meaning.
Bases were of the high penetration or 'culverin' type.
For example, if a PC is hiding in a 10×10 wooden shack that is hit by a culverin inflicting 35 points of damage on the structure, he may take 8 points of fragment damage if he fails his save.
Small culverin 2,000 gp 4d10 2000 lbs. 150 ft. Light 2 3/2
Small Culverin: Also known as the demi-culverin, this weapon fires a 10 lb shot and is suitable for mounting on many ships, including on the top deck.
Taking the Stormwrack method of doing ship damage, where e.g. a caravel has 24 hull sections with hardness 5 and 80 hp each, and six must be destroyed to sink the ship – it requires 3-4 good hits with a culverin to destroy one 10x10x10 section.
The ships are 200 yards apart, which is three range increments out for the culverin (-6 range).
And for "traditional" muzzleloader types we could issue a commemorative culverin with Bilbo Baggins face etched into it.