The Collaborative International Dictionary of English v.0.48:
Imperil \Im*per"il\, v. t. [imp. & p. p. Imperiledor Imperilled; p. pr. & vb. n. Imperiling or Imperilling.] To bring into peril; to endanger. [1913 Webster]WordNet (r) 3.0 (2006):
imperil v 1: pose a threat to; present a danger to; "The pollution is endangering the crops" [syn: endanger, jeopardize, jeopardise, menace, threaten, imperil, peril]