The Collaborative International Dictionary of English v.0.48:

Oppugnant \Op*pug"nant\, a. [L. oppugnans, p. pr. of oppugnare.
   See Oppugn.]
   Tending to awaken hostility; hostile; opposing; warring.
   "Oppugnant forces." --I. Taylor. -- n. An opponent. [R.]
   --Coleridge.
   [1913 Webster]