Source : Webster's Revised Unabridged Dictionary (1913)

Costeaning \Cos"tean`ing\, n.
   The process by which miners seek to discover metallic lodes.
   It consist in sinking small pits through the superficial
   deposits to the solid rock, and then driving from one pit to
   another across the direction of the vein, in such manner as
   to cross all the veins between the two pits.