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, but we advise using initial caps; see CMOS 7.86). 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 18th edition of CMOS (2024) unless otherwise noted.]