Source : Webster's Revised Unabridged Dictionary (1913)

Imperil \Im*per"il\, v. t. [imp. & p. p. {Imperiled}or
   {Imperilled}; p. pr. & vb. n. {Imperiling} or {Imperilling}.]
   To bring into peril; to endanger.

Source : WordNet®

imperil
     v : pose a threat to; present a danger to; "The pollution is
         endangering the crops" [syn: {endanger}, {jeopardize}, {jeopardise},
          {menace}, {threaten}, {peril}]