Diamond and graphite are a giant covalent structure while nylon
and polythane are macromolecule. sometimes Silica or diamond are
describe as macrmolecule in cambridge marking scheme as well as in
examiners' report.
Although both conatin many strong covalent bonds (for eample
diamond and poly(ethene) but macromolecule is the correct
terminolgy for a polymer since it is made from monomers but not
graphite or diamond. So i think the term "macromolecule" should be
used with polymers only and not with giant covalent structures.
Macro = (super) large. By its broadest definition (based on
linguistics), a macromolecule is simply any (super) large molecule,
and hence includes both polymers and non-polymers.
To be precise, the term "polymeric macromolecule" (preferred) or
"macromolecular polymer" (less preferred) should be used to
describe polymers, rather than simply "macromolecule" (which is
vague, as some macromolecules are non-polymers).
In describing diamond and silicon dioxide, Cambridge doesn't
require the word "macromolecule" as a compulsory marking point, so
you don't have to include this word in your answer if you don't
like to use the word in this way.