Goaf \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} or {gob}, to remove the pillars of mineral matter previously left to support the roof, and replace them with props. --Ure.