It's easy to confuse the adverbawhile with the two-word noun phrasea while: the main difference between them is grammatical.

The adverb awhile (one word) means for a short time: "Stay awhile."

The noun phrase a while (two words) refers to a period of time: "I sat for a while and waited."

Also see the usage notes below.

Examples:

• Before removing the radiator cap, wait awhile for the engine to cool.
• I haven't been to a football game in a long while.

 

Usage Notes:

• "Awhile is an adverb, with the same meaning as the adverbial prepositional phrasefor a while: Let's rest awhile; Let's rest for a while. When for a while cannot be substituted for awhile, awhile should be a while: spend a while with me. When for occurs, awhile should not follow; Stay for awhile should be Stay for a while or Stay awhile."
  (Edward Johnson, The Handbook of Good English. Washington Square Press, 1991)
• "As a noun, spell it as two words: a while. As an adverb, spell it as one: awhile."
  (Bryan Garner, Garner's Modern American Usage. Oxford University Press, 2009)

Practice:

(a) "Life's short. If you don't look around once in _____ you might miss it."
(Ferris Bueller in the movie Ferris Bueller's Day Off, 1986)

(b) Merdine invited me to stay ____ longer, but it was getting late.

Answers to Practice Exercises<

Glossary of Usage: Index of Commonly Confused Words