filbert

Loosely (as used in the British Isles), a cultivated variant of the native hazel (Corylus avellana), such as the cultivar ‘Cosford’, which has a relatively long nut and a husk (involucre) so long that it entirely covers the nut. Alternatively, ‘filbert’ means Corylus maxima, a related species.

This definition is abridged from A – Z of tree terms: A companion to British arboriculture.
Read the preface. Order the book.