expeditionaries definition
It seems to me that the OED's definition of expeditionary as a noun relates to the other sense of expedition, the sense in which expedition relates to the verb expedite. Far be it from me to dismiss Wikipedia's use of expeditionaries as incorrect. It's obvious what is meant by the word, whether or not it's in dictionaries. I would say that people who use the word are using it in such a way that it follows the pattern of revolutionary: