Alcinoo poma dare (to give apples to Alcinŏus).
To carry coals to Newcastle; sending cider to Herefordshire. The orchards of Alcinŏus, King of Coreyra (Corfu), were famous for their fruits.
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Entry taken from Dictionary of Phrase and Fable, edited by the Rev. E. Cobham Brewer, LL.D. and revised in 1895.