Goaf
Goaf , noun
[Compare 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.
Collocations (1)
To work the goaf or To work the gob , to remove the pillars of mineral matter previously left to support the roof, and replace them with props. — Ure