I've recently seen a musical and, on the night I went, three roles were being played by understudies instead of the regular actors.
This term has always puzzled me, partly because I've never found a satisfactory translation for it in my native tongue. However, while I well understand its meaning and although I've researched various dictionaries, I haven't found clear indications of its origin. The Online Etymology Dictionary deals with the word in one line and the OALD, normally so generous with references to the origin of terms, doesn't even try.
Can anyone tell me how this word came into existence?