Word Study
    Goaf
CIDE DICTIONARY
Goaf, n. [Cf. 1st Gob.]. 
                                            
                                         That part of a mine from which the mineral has been partially or wholly removed; the waste left in old workings; -- called also gob  .                                                                                 [1913 Webster]                                                                                                                    
                                                                                    
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