verb (used with object)
to be wary, cautious, or careful of (usually used imperatively): Beware such inconsistency. Beware his waspish wit.
verb (used without object)
to be cautious or careful: Beware of the dog.
Origin of beware
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
(usually used in the imperative or infinitive, often foll by of) to be cautious or wary (of); be on one's guard (against)
Word Origin for beware
C13 be war, from be (imperative) + war wary
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
c.1200, probably from a conflation of be ware (though the compound bewarian "defend" existed in Old English). See wary.
Online Etymology Dictionary, © 2010 Douglas Harper