tuff

from WordNet (r) 3.0 (2006)
tuff
    n 1: hard volcanic rock composed of compacted volcanic ash [syn:
         {tuff}, {tufa}]
    
from The Collaborative International Dictionary of English v.0.48
Tuff \Tuff\, n. (Min.)
   Same as {Tufa}.
   [1913 Webster]
    

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