Definition of "filbert"

I'll bring thee / To clust'ring filberts, and sometimes I'll get thee / Young scamels from the rock.

1610–1611 (date written), William Shakespeare, “The Tempest”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act II, scene ii]

I've seen one monkey force open the jaws of his brother, resolutely introduce his fingers, pluck from the sanctuary of his cheek the filbert he had just stowed there for his private nutrition and delight, and crunch and eat it with a stern ecstasy of selfishness, himself […]

1863, Sheridan Le Fanu, The House by the Churchyard