Hazelnut n. : The nut of the hazel.

Example:
What are the origins of Hazelnut coffee?

Taxonomy
Hazelnut, nuts, harvester, shell, leaves, Hazelnut Production, Levant, ground, sweeper, tree, Hazelnut oil, Turkish, Giresun, orchard, fallen nuts, Hazel nuts, pit, cultivars.

Defination from the web:
hazelnut is the nut of the hazel and is also known as a cob nut or filbert nut according to species. ... The name "hazelnut" applies to the nuts of any of the species of the genus Corylus. This hazelnut, the kernel of the seed, is edible and used raw or roasted, or ground into a paste. ...