a different kettle of fish
be a different kettle of fish
To be entirely different in scope or description from someone or something that was just being discussed. Steve: "So you like your first two roommates, but what about your third one?" Joe: "William? Oh, he's a different kettle of fish altogether." I suppose we could start looking at buying a house now that our baby is on the way, but that's an entirely different kettle of fish!
a different kettle of fishor
another kettle of fishBRITISH
COMMON You say that something is a different kettle of fish or another kettle of fish to emphasize that it is completely unlike another thing that you are mentioning. Artistic integrity? Who needs it? Money? Now that's a completely different kettle of fish. Howard was a sweetheart. But Clarisse was another kettle of fish.
a different kettle of fisha completely different matter or type of person from the one previously mentioned. informal
1993 Empire Meryl is the finest actress of her generation but Arnold is, er, a different kettle of fish.
a different kettle of ˈfish(informal) a person or thing that is completely different from somebody/something else previously mentioned: You may be able to read French well, but speaking it fluently is a different kettle of fish entirely.
A kettle in this idiom is a pan in which you can cook a whole fish.