Meaning of demi-cannon

dem•i-can•non

Pronunciation: (dem"ē kan'un), [key]
— n.
  1. a large cannon of the 16th century, having a bore of about 6 in. (17 cm) and firing a shot of from 30 to 36 lb. (14 to 16 kg).
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.