Third-person singular form of beware; to be cautious or on guard against something dangerous or unpleasant.
From 'be-' plus 'ware' (archaic form of 'aware'). The verb 'beware' dates to Middle English and means literally to 'be aware' or to take care against something.
'Beware the Ides of March!' is probably the most famous use of this word in English literature. Despite being archaic, 'beware' survives in fixed phrases and warnings, while most other 'be-' + verb constructions vanished.
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