horse of a different color

Something completely different or separate, especially in comparison to something else. I've always found math to be easy, but calculus is a horse of a different color.

Common Names:

Name	Pronounced	Usage
Riny	-	Dutch
Xavier	ZAY-vee-ər (English), ZAY-vyər (English), ig-ZAY-vee-ər (English), za-VYE (French), sha-VYER (Portuguese)	English, French, Portuguese, Catalan, Spanish (Archaic)
Clematis	klə-MAT-is	English (Rare)
Laurits	-	Danish, Norwegian
Joscelin	-	Old Norman
Hannie	HAHN-nee	Dutch