Can even have different meanings regionally. A gill is ¼-pint -- so defined in Wikipedia &c. But if you ask for "a gill" in a Northern English pub, you will be served a ½-pint; which appears to be its meaning in some versions of 'The Barley Mow'. Roma Gill, the late Marlovian & Shakespearean editor, who was a friend of mine at Cambridge, came from Keighley in Yorkshire, & told me once that her nickname at home among friends in the Bradford Civic Playhouse &c, was "halfpint".

~M~