Sentence:  I did not even know what a ‘<WSD>pony</WSD>', a small chaser of beer, was. But of course I could not admit that. So putting on an air of nonchalance, and a deep voice, I strolled into a pub with one of the other equally naive guys and we ordered two ponies of beer. / ‘McEwans?' asked the barman. / ‘Naw - ponies' said I. 
Meaning of the word marked with <WSD> tags:  A small serving of an alcoholic beverage, especially beer.