The Collaborative International Dictionary of English v.0.48:

Endamage \En*dam"age\ (?; 48), v. t. [imp. & p. p. Endamaged
   (?; 48); p. pr. & vb. n. Endamaging.] [Pref. en- + damage:
   cf. F. endommager.]
   To bring loss or damage to; to harm; to injure. [R.]
   [1913 Webster]

         The trial hath endamaged thee no way.    --Milton.
   [1913 Webster]