One of the mysteries of the English language finally explained.
Any of the feathers of a peacock; specifically one of the long feathers forming the tail coverts, having an iridescent eye-like marking towards the end. (Used figurative as a symbol of ostentation or vainglory.).
Late Middle English; earliest use found in Mandeville's Travels. From the genitive of peacock + feather.
peacock's feather/ˌpiːkɒks ˈfɛðə/
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