We don't have synonyms for tompion yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are pompion, tampion and tompon.
(n) :
Alternative spelling of tampion. [A wooden plug, or a metal or canvas cover, for the muzzle of a gun, cannon, or other piece of ordnance when not in use; a stopper; a bung.]
(n) :
Alternative spelling of tampion. [A wooden plug, or a metal or canvas cover, for the muzzle of a gun, cannon, or other piece of ordnance when not in use; a stopper; a bung.]