A mining term for a shallow pit or trench dug to test for ore deposits, or to dig such test pits.
From Cornish costan or related Celtic mining terminology, used in Cornish tin mining from medieval times, with Cornish miners spreading the term across Britain.
This Cornish mining word survived because those miners were legendary—costeaning (test mining) helped Britain find tin and copper, and the English language absorbed the term from these specialized workers.
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