Excellent, outstanding, or remarkable; a British expression meaning something is very good or impressive.
Present participle of 'cork' (to seal or close) used as an adjective, becoming British slang by the late 19th century. The meaning shifted from 'something that seals the deal' to 'something excellent'.
British slang 'corking' is almost extinct now, but it survived in phrases like 'corking good shot' because it perfectly captures excitement—and it's definitely more fun to say than 'excellent'!
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