[1] : The Collaborative International Dictionary of English v.0.48

off-guard \off-guard\ pred. adj.
   not watching for possible danger; not alert; as, caught in an
   off-guard moment.
   wordnet 1.5

[2] : WordNet (r) 2.0

off-guard
     adj : not prepared or vigilant; "the blow caught him napping";
           "caught in an off-guard moment"; "found him off his
           guard" syn: napping, off-guarda, off guardp,
            off one's guardp, off his guard, off her guard,
            off your guard
see also:
napping off-guarda off guardp off one's guardp off his guard off her guard 
off your guard 

Off-Guard >> O Words
Off-Guard, definition of term: Off-Guard
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