No rule for this one
No ending or word group predicts the article of Urlaub. Learn it as a pair and say it out loud: der Urlaub.
der Urlaub
It's der Urlaub. Urlaub is masculine, plural die Urlaube.
Im August habe ich Urlaub.
In August I'm on holiday.
Im Urlaub fahre ich nach Hause.
On holiday I go home.
Wo warst du im Urlaub?
Where were you on holiday?
No ending or word group predicts the article of Urlaub. Learn it as a pair and say it out loud: der Urlaub.