Slight different than hyphenating. Also, I know someone posted a website where you can look these up. If someone could list it again, I would really appreciate it and I promise to bookmark it.
Anyway, you know lots of words out there and you don't know whether it's one word or two. And sometimes it's industry specific. So in regular use, it would be one word, but in the specific industry it would be two. Anyhoo , , ,
lead man (I think two)
seat belt (always two, but I always think it should be one)
I'm sure there are tons out there. Feel free to share or ask.