The Collaborative International Dictionary of English v.0.48:

Quadra \Quad"ra\, n.; pl. Quadr[ae]. [L., a square, the socle,
   a platband, a fillet.] (Arch.)
   (a) The plinth, or lowest member, of any pedestal, podium,
       water table, or the like.
   (b) A fillet, or listel.
       [1913 Webster]