Is there such thing as a 3D hexagon?

Yes!!!!

It's names a 'HEXAHEDRON'.

A CUBE is one such object.

NB

In the nomenclature (naming system).

'Hexa' is '6' from Latin.

'--gon' is a 2 dimensional figure. (As IN POLYGON ; many sides).

'--hedron- is a 3 dimensional solid. (As in POLYHEDRON ; many faces).