'''Warn''' is to give notice to beforehand especially of danger or [[evil]].
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To '''warn''' is to give notice to someone beforehand, especially of danger or [[evil]]. This can either be an urgent warning about impending trouble ("Don't step back!") or direction to avoid future trouble ("Don't buy that, it won't last long.")<ref>http://www.merriam-webster.com/dictionary/warn</ref>