1) The nut of the cultivated hazel or the tree itself.
Said to be so named because the nut was ripe close to St Philibert’s day, that is 22 August, old style: 1476 ‘cut and carried away filberts’, Yeadon
1584 20s and 1 pecke fylbertes at two times in the year, Howden
1642 nutte-trees and filbert-trees, Elmswell
1735 stealing Philberts.