Why is the ninth month called September?
"barrel or cask for soap or liquor; iron vessel," c.1400, from Old French ponchon, ponson "wine vessel" (13c.), of unknown origin. Uncertain connection with puncheon "slab of timber, strut, wooden beam used as a support in building" (mid-14c.). Punch (n.2) in the drink sense is too late to be the source of the "cask" sense.
"pointed tool for punching or piercing" used by masons, also "die for coining or seal-making," mid-14c.; see punch (n.1). Meaning "stamp, die" is from c.1500, a specialized use.