Belch is the name of a character in Twelfth Night, Sir Toby
Belch. But belch meant then what it means now. The name was
intended to suggest the kind of man who drinks to excess and burps.
Sir Toby does this in fact in the play, covering it up with "A
plague o' these pickled herring!" Nobody is fooled, however: they
know that booze and not pickled herring is at fault.