Earnest, you have actually answered my long time question. I'm not a native speaker of English as you know, and I felt rather strange about that English-speaking people use plural forms such as “a pair of glasses” or “pants”. Because this naturally (for non-native speakers of English at least) raises a question what people would call each of a broken pair of pants or glasses, if they are broken into two halves. The logical answer for me seemed to be a pant or a glass (for me). Now I know what you call one.

Satoshi