filbert vs hazelnut

filbert and hazelnut both are nouns.

Word	Noun	Adjective	Verb	Adverb
filbert	Yes	No	No	No
hazelnut	Yes	No	No	No

As nouns, filbert and hazelnut are synonyms defined as:

Other synonyms of filbert include cob, cobnut.

As nouns, hazelnut is a hypernym of filbert; that is, hazelnut is a word with a broader meaning than filbert:

filbert: small nut-bearing tree much grown in Europe
hazelnut: any of several shrubs or small trees of the genus Corylus bearing edible nuts enclosed in a leafy husk

Other hypernyms of filbert include hazel, hazelnut tree.

filbert (noun)	hazelnut (noun)
nut of any of several trees of the genus Corylus	nut of any of several trees of the genus Corylus
small nut-bearing tree much grown in Europe	any of several shrubs or small trees of the genus Corylus bearing edible nuts enclosed in a leafy husk