the GNU version of the Collaborative International Dictionary of English
n. The vent of a cannon or other firearm, by which fire is communicateed to the powder of the charge.
The Century Dictionary and Cyclopedia
n. A small tubular opening through the thickness of the barrel of a gun, cannon, or pistol, by means of which fire is communicated to the charge within.
Word Usage
"It was loaded to the muzzle; but just as the pilot was about to apply a red-hot coal to the touchhole, Mr. Fogg said, “Hoist your flag!”"