Nouns ending in -ude are usually feminine.
The suffix marks an abstract state or quality.
Is attitude masculine or feminine?
l'attitude
The rule behind it
92% of -ude nouns are feminine
In context
Son attitude n'est pas du tout polie.
His attitude is by no means polite.
Il adoptait une attitude agressive à mon égard.
He assumed an aggressive attitude toward me.
Ce qui me préoccupe, c'est son attitude.
What bothers me is his attitude.