What is Walnut?
Walnut is (noun) 1. a hard round nut with a shell which has a lot of folds on its surface He cracked the walnuts with the nutcrackers. A scoop of maple and walnut ice cream. 2. a tree on which walnuts grow The walnuts or walnut trees have produced a huge crop this year. 3. wood from a walnut tree The beautifully dark walnut panelling in my office.
source: Easier English, Student Dictionary Upper Intermediate Level