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]

The Collaborative International Dictionary of English v.0.48:

endangered \en*dan"gered\, a.
   1. Being in a condition or situation where life or serious
      harm is possible; in danger; at risk.
      [PJC]

   2. Small in numbers, with significant possibility of
      extinction; -- of species.
      [PJC]

WordNet (r) 3.0 (2006):

endangered
    adj 1: (of flora or fauna) in imminent danger of extinction; "an
           endangered species"