cobnut vs hazelnut tree

cobnut and hazelnut tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
cobnut	Yes	No	No	No
hazelnut tree	Yes	No	No	No

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

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

Other hypernyms of cobnut include hazel, hazelnut.

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