The Collaborative International Dictionary of English v.0.48:

Gravel \Grav"el\, n. [OF. gravele, akin to F. gr?ve a sandy
   shore, strand; of Celtic origin; cf. Armor. grouan gravel, W.
   gro coarse gravel, pebbles, and Skr. gr[=a]van stone.]
   1. Small stones, or fragments of stone; very small pebbles,
      often intermixed with particles of sand.
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   2. (Med.) A deposit of small calculous concretions in the
      kidneys and the urinary or gall bladder; also, the disease
      of which they are a symptom.
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   Gravel powder, a coarse gunpowder; pebble powder.
      [1913 Webster]