from The Century Dictionary and Cyclopedia
- n. A hole, drilled in metal, of such a diameter that a full screw-thread may be tapped within it, the tapping cutting away only the metal required to form such a thread. Its diameter is therefore smaller than the nominal diameter of the tap or the screw to be inserted, by twice the depth of the thread.
- n. Same as tap-hole.
Sorry, no etymologies found.