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]