We say (a pair of) trousers, (a pair of) scissors. For these two particular words, is/was there something like "a trouser" or "a scissor"? Did it use to mean anything?
E.g. in Czech, the word for scissors is also plural but is derived from "knives". So I was wondering if the pair-words like these are derived from some (now forgotten) words with a meaning in singular. Similarly, the Slovak word for trousers is a plural of a Czech word meaning "a single trouser leg". (Czech and Slovak are very close.)