Goaf (?); n.; pl.Goafs (#) or Goaves (#). [Cf. 1st 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 goaforgob, to remove the pillars of mineral matter previously left to support the roof, and replace them with props. Ure.