You Could Look It Up

Q. Would you ever use “styleguide” as a single word?

A. Probably only in a hashtag—#StyleGuide or #styleguide (hashtags aren’t case sensitive, and Chicago style allows for either). Guide, unlike book, doesn’t tend to form one word unless it’s at the beginning. So style guide but stylebook and guidebook. For answers to questions like this one, Merriam-Webster is our go-to guide.

[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]