goaf

Goaf; n.; pl. Goafs or Goaves. Etym: [Cf. lst Gob.] (Mining) Defn: 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.

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