The Collaborative International Dictionary of English v.0.48:

Counterbrace \Coun"ter*brace`\, v. t.
   1. (Naut.) To brace in opposite directions; as, to
      counterbrace the yards, i. e., to brace the head yards one
      way and the after yards another.
      [1913 Webster]

   2. (Engin.) To brace in such a way that opposite strains are
      resisted; to apply counter braces to.
      [1913 Webster]