But panto is short for pantomime,

But, but! (hands waving wildly in air) what about the "mime" part...I thought mime had to do with "silent"

Wait! Wait! The OED says pantomime is a performance of ludicrous representations of familiar characters, then it goes on about mime as conveying words using only gestures and movement.
Oh, well!
So much for a shared language!
And "clarifications."