Goaf (?); n.; pl. Goafs (#) or Goaves (#). [Cf. lst Gob.] Mining
That part of a mine from which the mineral has been partially or wholly removed; the waste left in old workings; -- called also gob .
To work the goaf ∨ gob, to remove the pillars of mineral matter previously left to support the roof, and replace them with props. Ure.
© Webster 1913.