Source : Webster's Revised Unabridged Dictionary (1913)

Caponiere \Cap`o*niere"\, n. [F. caponni[`e]re, fr. Sp.
   caponera, orig., a cage for fattening capons, hence, a place
   of refuge; cf. It. capponiera. See {Capon}.] (Fort.)
   A work made across or in the ditch, to protect it from the
   enemy, or to serve as a covered passageway.