The Collaborative International Dictionary of English v.0.48:

Rubble \Rub"ble\, n. [From an assumed Old French dim. of robe
   See Rubbish.]
   1. Water-worn or rough broken stones; broken bricks, etc.,
      used in coarse masonry, or to fill up between the facing
      courses of walls.
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            Inside [the wall] there was rubble or mortar.
                                                  --Jowett
                                                  (Thucyd.).
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   2. Rough stone as it comes from the quarry; also, a
      quarryman's term for the upper fragmentary and decomposed
      portion of a mass of stone; brash. --Brande & C.
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   3. (Geol.) A mass or stratum of fragments or rock lying under
      the alluvium, and derived from the neighboring rock.
      --Lyell.
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   4. pl. The whole of the bran of wheat before it is sorted
      into pollard, bran, etc. [Prov. Eng.] --Simmonds.
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   Coursed rubble, rubble masonry in which courses are formed
      by leveling off the work at certain heights.
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