A pit or trench sunk through surface deposits in order to locate a vein of ore and ascertain its extent.
Late 18th century; earliest use found in William Pryce (d. 1790), surgeon, mineralogist, and antiquary. Origin uncertain; perhaps from an otherwise unattested Cornish phrase or compound from a first element of uncertain origin + sten tin (Middle Cornish stean; cognate with Welsh ystaen).
verbSouth West English Mining
To sink a costean.
Mid 19th century; earliest use found in Cornwall Royal Gazette. From costean.