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The Collaborative International Dictionary
Countermuring

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

Wiktionary
countermuring

vb. (present participle of countermure English)