Walnut

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late Old English walh-hnutu, from a Germanic compound meaning ‘foreign nut’.

wiktionary

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From Middle English walnote, walnutte, walnotte, walnote, from Old English wealhhnutu(“walnut”, literally “foreign nut”), from Proto-Germanic *walhaz(“foreigner”) + *hnuts(“nut”). Cognate with Dutch walnoot, German Walnuss, Swedish valnöt, Icelandic valhneta. Compare more recent term Welsh onion, which also uses Welsh to mean “foreign”.

etymonline

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walnut (n.)

Old English walhnutu "nut of the walnut tree," literally "foreign nut," from wealh "foreign" (see Welsh) + hnutu (see nut). Compare Old Norse valhnot, Middle Low German walnut, Middle Dutch walnote, Dutch walnoot, German Walnuss. So called because it was introduced from Gaul and Italy, distinguishing it from the native hazel nut. Compare the Late Latin name for it, nux Gallica, literally "Gaulish nut." Applied to the tree itself from 1600 (earlier walnut tree, c. 1400).