De or het wintervastheid?

The correct Dutch article is:

de wintervastheid

Rule Words ending in -heid: almost always de. See the rule

How to use wintervastheid

the wintervastheidde wintervastheid
this wintervastheiddeze wintervastheid
that wintervastheiddie wintervastheid
our wintervastheidonze wintervastheid
your wintervastheidjouw wintervastheid
every wintervastheidelke wintervastheid
which wintervastheid?welke wintervastheid?
a big wintervastheid / the big wintervastheideen grote wintervastheid, de grote wintervastheid