The Collaborative International Dictionary of English v.0.48:
Oppugn \Op*pugn"\, v. t. [imp. & p. p. Oppugned; p. pr. & vb. n. Oppugning.] [OF. oppugner, L. oppugnare; ob (see Ob-) + pugnare to fight. See Impugn.] To fight against; to attack; to be in conflict with; to oppose; to resist. [1913 Webster] They said the manner of their impeachment they could not but conceive did oppugn the rights of Parliament. --Clarendon. [1913 Webster]