Sentence:  The tragic irony of the play is that the very belief in and concern with a devil who could be met in the woods and combatted with formulae set out in books was the very thing that prevented them from detecting the real <WSD>devil</WSD> when he came among them . 
Meaning of the word marked with <WSD> tags:  (Judeo-Christian and Islamic religions) chief spirit of evil and adversary of God; tempter of mankind; master of Hell