No rule for this one
No ending or word group predicts the article of Cousin. Learn it as a pair and say it out loud: der Cousin.
der Cousin
It's der Cousin. Cousin is masculine, plural die Cousins.
Mein Cousin arbeitet in Dubai.
My cousin works in Dubai.
No ending or word group predicts the article of Cousin. Learn it as a pair and say it out loud: der Cousin.