De or het tenniskleding?

The correct Dutch article is:

de tenniskleding

Rule Words ending in -ing: almost always de. See the rule
Meaning (Dutch) gespecialiseerde sportkleding die is ontworpen om de prestaties, het comfort en de bewegingsvrijheid van een tennisser te optimaliseren.

How to use tenniskleding

the tenniskledingde tenniskleding
this tenniskledingdeze tenniskleding
that tenniskledingdie tenniskleding
our tenniskledingonze tenniskleding
your tenniskledingjouw tenniskleding
every tenniskledingelke tenniskleding
which tenniskleding?welke tenniskleding?
a big tenniskleding / the big tenniskledingeen grote tenniskleding, de grote tenniskleding

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