The Collaborative International Dictionary of English v.0.48:

Retund \Re*tund"\, v. t. [L. retundere, retusum; pref. re- re- +
   tundere to beat.]
   To blunt; to turn, as an edge; figuratively, to cause to be
   obtuse or dull; as, to retund confidence. --Ray. Cudworth.
   [1913 Webster]