IPA: /ˈtæmpɪən/
KK: /ˈtæmpɪən/
A cover or plug used to seal the opening of a cannon or gun to prevent dust and moisture from entering.
The soldiers placed a tampion in the cannon's muzzle to protect it from the rain.
Tampion originates from Old French 'tampon', meaning a plug or stopper. It refers specifically to a device used to block the muzzle of a cannon or firearm, preventing debris from entering.
Think of a 'plug' ('tampon') that stops something from getting in — that's why a tampion is used to block the muzzle.