room-and-pillar

[room-uh n-pil-er, roo m-]

adjective Mining.

noting a means of extracting coal or other minerals from underground deposits by first cutting out rooms, then robbing the pillars between them; pillar-and-breast.

Compare longwall.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019