be another kettle of fish

another kettle of fish

Any issue or matter that is entirely different in scope, description, or nature from that which was just being discussed. A: "So you like your first two roommates, but what about your third one?" B: "William? Oh, he's another kettle of fish altogether." I suppose we should start looking at buying a house now that our baby is on the way, but that's another kettle of fish! I know you think you're some hotshot just because you worked in television once, but working on a film is a another kettle of fish.

be another kettle of fish

To be entirely different in scope or description from someone or something that was just being discussed. A: "So you like your first two roommates, but what about your third one?" B: "William? Oh, he's another kettle of fish altogether." I suppose we should start looking at buying a house now that our baby is on the way, but that's another kettle of fish!