To make something dirty, unclean, or morally bad; to contaminate.
From 'be-' plus 'foul' (Old English 'ful,' related to German 'faul' meaning rotten). The prefix 'be-' intensifies the meaning of foul, literally meaning 'to make foul.'
Unlike many 'be-' words that are archaic, 'befoul' is still actively used—especially in environmental and moral contexts—because it expresses intense contamination both physically and metaphorically with an elegant single verb.
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