From Longman Dictionary of Contemporary Englishwalnutwal‧nut /ˈwɔːlnʌt $ ˈwɒːl-/ noun 1 
[countable]DF a nut that you can eat, shaped like a human brain coffee and walnut cake2 [countable] (also walnut tree)HBP a tree that produces this type of nut3 [uncountable]TIDHF the wood from a walnut tree, often used to make furniture
[countable]DF a nut that you can eat, shaped like a human brain coffee and walnut cake2 [countable] (also walnut tree)HBP a tree that produces this type of nut3 [uncountable]TIDHF the wood from a walnut tree, often used to make furnitureExamples from the Corpus
walnut• I walked down the highway to Sabinal, eating black walnuts from the walnut tree.• Add the chopped prunes, apricots, apples, raisins and broken walnuts and cook gently until the fruits plump up.• The dressing-table mirror is made from walnut.• The surprise is the layer of ground walnuts, a la baklava, in the bottom of the cup.• Jaguar sells its leaping kitty hood ornaments mounted on a block made from the walnut that goes into its dashboards.• Victorian walnut writing box, £100; large quantity of books, £100.• It led to a five-foot-wide walnut staircase that swept up in a sumptuous curve to the floor above.• Place in a bowl with walnuts and sultanas.Origin walnut Old English wealhhnutu, from Wealh “Welsh person, foreigner” + hnutu “nut”; because it was brought into Britain from abroad, probably by the Romans 