GOAF

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 goaf or gob, to remove the pillars of mineral matter previously left to support the roof, and replace them with props. Ure.