The Collaborative International Dictionary of English v.0.48:

Impugnation \Im`pug*na"tion\, n. [L. impugnatio: cf. OF.
   impugnation.]
   Act of impugning; opposition; attack. [Obs.]
   [1913 Webster]

         A perpetual impugnation and self-conflict. --Bp. Hall.
   [1913 Webster]