This is purely a curiosity, but I'm fascinated by mid-word pluralization, even if the word in question is a compound word.
For example, passersby or standersby.
No others have occurred to me. Can you provide other examples, or a link to a resource that enumerates them?
I'm particularly interested in compounds that do not include spaces or hyphens.
Best Answer
It could be any compound noun of which the head, the "main noun", is not the final part of the compound. This includes all compound nouns whose final parts are not nouns. "Bystanders" is normally not written as you did. In "passers-by", the final part is "by", which is not a noun. Note that there might be some controversy about the correct spelling of some such words, but I just try to be consistent. A few examples: