The Collaborative International Dictionary of English v.0.48:

Countermure \Coun`ter*mure"\ (koun`t?r-m?r"), v. t. [imp. & p.
   p. Countermured (-m?rd"); p. pr. & vb. n. Countermuring.]
   [Cf. F. contremurer.]
   To fortify with a wall behind another wall. [R.] --Kyd.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Countermure \Coun"ter*mure`\ (-m?r`), n. [Counter- + mure: cf.
   F. contremur.] (Fort.)
   A wall raised behind another, to supply its place when
   breached or destroyed. [R.] Cf. Contramure. --Knolles.
   [1913 Webster]