The Collaborative International Dictionary of English v.0.48:

Endanger \En*dan"ger\, v. t. [imp. & p. p. Endangered; p. pr.
   & vb. n. Endangering.]
   1. To put to hazard; to bring into danger or peril; to expose
      to loss or injury; as, to endanger life or peace.
      [1913 Webster]

            All the other difficulties of his reign only
            exercised without endangering him.    --Burke.
      [1913 Webster]

   2. To incur the hazard of; to risk. [Obs.]
      [1913 Webster]

            He that turneth the humors back . . . endangereth
            malign ulcers.                        --Bacon.
      [1913 Webster]

WordNet (r) 3.0 (2006):

endanger
    v 1: pose a threat to; present a danger to; "The pollution is
         endangering the crops" [syn: endanger, jeopardize,
         jeopardise, menace, threaten, imperil, peril]
    2: put in a dangerous, disadvantageous, or difficult position
       [syn: queer, expose, scupper, endanger, peril]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "endanger":
   chance, compromise, encounter danger, expose, gamble, gamble with,
   hazard, imperil, incur danger, jeopard, jeopardize, jeopardy,
   lay open, menace, peril, put in danger, put in jeopardy, risk,
   threaten, venture