Can "fast" be used as an adjective?

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<p>EDIT: SORRY ABOUT THE TITLE I MEANT ADVERB. >__<</p>

<p>Just a really quick writing question. Can "fast" be an adverb?</p>

<p>For example, can I say "he ran fast" instead of "he ran quickly"?</p>

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<p>Yep, it is fine.</p>

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<p>Yes, “fast” can be an adverb. “fastly” means something else.</p>

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<p>^^^ how do you use “fastly” ??</p>

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<p>According to Webster’s, “fastly” means firmly or surely.</p>