Compound

A compound is a phrase which is composed of two words, but with a single meaning. It may, or may not, be hyphentated.

An important point to bear in mind is that the spelling and word stress may vary depending on whether the compound is being used as a verb, adjective or noun. So we write It was a smooth take-off vs We'll take off in a minute, or roller coaster as a noun but roller-coaster (or roller-coast) as a verb.