What does "bosh" mean?

Bosh: One of the sloping sides of the lower part of a blast furnace; also, one of the hollow iron or brick sides of the bed of a puddling or boiling furnace.

Additional senses

  1. 2.pl. The lower part of a blast furnace, which slopes inward, or the widest space at the top of this part.
  2. 3.In forging and smelting, a trough in which tools and ingots are cooled.

Sources