[found on grammarist.com]
Have you ever been writing, and realized you have no idea what words you need—nor if they are a single word, two words, or a compound word? This site, grammarist.com, is an amazing tool for just such a panic attack. Take a look at the example for workout vs. work out:
“Workout vs. work out
As a noun or an adjective, workout is one word. As a verb, it’s two words—work out. So, for instance, when it’s workout time, you start your workout, work out for a while, and stop.
Work out is just one of many phrasal verbs with corresponding one word forms that function as nouns and adjectives. The one-word forms are sometimes hyphenated (e.g., work-out), but more often completely compounded. These forms never catch on as verbs in edited writing, though they are often erroneously treated as verbs in more informal contexts.”
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