There are 2 results of your search for middy2.
middy1
A medium sized glass of beer (approx 285ml) served in NSW; equivalent to a pot: A middy of New thanks barman. Compare butcher, glass, handle, middy2, pony, pot, schooner1, schooner2, seven. [so called because it is midway between a glass and a schooner]
middy2
a small glass of beer (approx. 200ml) served in WA; equivalent to a pony. Compare butcher, glass, handle, middy1, pony, pot, schooner1, schooner2, seven. [so called because it is midway between a glass and a pot]