De or het onlineverslaving?

The correct Dutch article is:

de onlineverslaving

Rule Words ending in -ing: almost always de. See the rule
Meaning (Dutch) (medisch, psychologie) verslaving aan het online op internet zijn

How to use onlineverslaving

the onlineverslavingde onlineverslaving
this onlineverslavingdeze onlineverslaving
that onlineverslavingdie onlineverslaving
our onlineverslavingonze onlineverslaving
your onlineverslavingjouw onlineverslaving
every onlineverslavingelke onlineverslaving
which onlineverslaving?welke onlineverslaving?
a big onlineverslaving / the big onlineverslavingeen grote onlineverslaving, de grote onlineverslaving

Meaning, plural, diminutive, pronunciation and translations: WikiWoordenboek (Dutch Wiktionary) (CC BY-SA 4.0). Example sentences: Tatoeba (CC BY 2.0 FR).