From m-w.com:
word
2 a (1) : a speech sound or series of speech sounds that symbolizes and communicates a meaning without being divisible into smaller units capable of independent use
Hmm. Nothing about "egregore" in the Oxford English Dictionary, either. I suppose it's not used widely enough outside of magickal literature (tho' they've got some pretty obscure stuff in there...).
The term egregore is derived from a Greek word meaning "to be aware of" or "to watch over". An egregore is commonly understood to be magical entity purposefully created by a group or order as an encapsulation of the group's collective aspirations and ideals.
Its a word you won't find much in dictionaries, largely from being too new. Dictionaries take a bit before a word in use is accepted into the language. So, if you use it in any officialish writing, you'll need to include a definition like the one above as it is a specialized term.
I had always assumed that "i grigori" was the root of "egregore."
Forgive me as I'm cloudy on the details...There was some level of angelic beings I learned about in a long-ago scripture class which were called the "i grigori," a name which meant "watchers." I'm guessing maybe this came from the Book of Enoch?