Linked from
The 10 pages that link to Nut (fruit), each with the reason it gives.
DrupeCompared with: A drupe has a fleshy fruit region; a true nut is dry throughout.
AcheneCompared with: A nut is generally larger and has a harder fruit wall than an achene.
AcornNarrower topic: An acorn is botanically a nut, though not a true nut in culinary usage.
BetulaceaeRelated: Hazelnuts and several other Betulaceae fruits are nuts in the botanical sense.
CupuleRelated: Many cupules surround nuts, but the cupule is separate from the nut's fruit wall.
FagalesRelated: Several Fagales produce nuts, including hazelnuts, beechnuts, and walnuts.
HazelnutNarrower topic: Botanically, a hazelnut is a true nut of this fruit type.
Carya laciniosaRelated: Its edible seed is enclosed in a thick-walled hickory nut.