Lewis Short
rūdus (noun N) :
* Stones broken small and mingled with lime for plastering walls, paving floors, etc.
* In gen., Vitr. 7, 1: rudus inicere solo,Plin. 36, 25, 62, § 186; Pall. 1, 9, 4; 11, 2 Mai: aedificia tecta rudere aut pavimentis, Auct. B. Alex. 1, 3: rudere, non tegulis teguntur, Auct. B. Hisp. 8, 2: pingue, i. e. rich soil, Col. poët. 10, 81.
* In partic., old rubbish, of the stones, plaster, etc., of decayed buildings (rare and not ante-Aug.): ruderi accipiendo Ostienses paludes destinabat,Tac. A. 15, 43.—In plur.: alveum Tiberis laxavit ac repurgavit, completum olim ruderibus,Suet. Aug. 30; id. Vesp. 8.
Charlton T. Lewis, Charles Short, A Latin Dictionary