be a different kettle of fish

a different kettle of fish

Any issue or matter that is entirely different in scope, description, or nature from that which 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!
See also: different, fish, kettle, of

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!
See also: different, fish, kettle, of
Farlex Dictionary of Idioms.

a different kettle of fish

or

another kettle of fish

BRITISH
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.
See also: different, fish, kettle, of
Collins COBUILD Idioms Dictionary, 3rd ed.

a different kettle of fish

a 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.
See also: different, fish, kettle, of
Farlex Partner Idioms Dictionary

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.
See also: different, fish, kettle, of
Farlex Partner Idioms Dictionary
See also:
  • a different kettle of fish
  • kettle
  • be another kettle of fish
  • another kettle of fish
  • be a whole other kettle of fish
  • another pair of shoes
  • another story
  • answer to the description (of)
  • answer to the description of
  • scope out
References in periodicals archive
The Palace boss said: "If I was to allow my true personality and emotions to take over, it would be a different kettle of fish.
Tuohy said: "Wales will be a different kettle of fish, they've had a bit of a 'feeler' game against Italy.
Now if he should offer Guisborough and Nunthorpe instead, well that would be a different kettle of fish, at least we could get on with building the East Middlesbrough Relief Road.
"It will be a different kettle of fish and there will be different expectations."
But next Sunday I think is going to be a different kettle of fish.'
"When confronted with burglars on your property in the middle of the night it might be a different kettle of fish for people who tell researchers they would do a Tony Martin.