If you said that something was “a different kettle of fish” or “another kettle of fish”, you would mean that it’s something else altogether, and very different to what you have been discussing. At least in the UK.
This expression dates from the late 19th century, and is/was most common in Scotland and northern England. Before then, fish kettles featured in the phrase “a pretty kettle of fish”, which means “a muddle or awkward state of affairs”.
A fish kettle (see below) is type of long saucepan used since the 17th century to poach fish, especially large fish like salmon.
Appartently in the USA you might say that it’s “quite another story”, “a whole different story”, “a different ball game” or “a horse of a different color. Are there others?
Equivalents of these idioms in French include “c’est une autre paire de manches” (it’s another pair of sleeves”) and “c’est une toute autre histoire” (it’s a whole other story). Do you know of others in French or other languages?
Sources: Reverso, The Phrase Finder
In the US you can often get “a whole nother story”. (sic)
I’m pretty sure “a horse of a different color” has fallen out of use. The only time I can remember encountering that one is in an L. Frank Baum book.
In Spain we say “es harina de otro costal”, which means “it’s from another flour sack” (or, literally, “it’s flour from another sack”).
“Kettle of fish” is used in the US, too. And yes, “a whole nother story.” Who says English doesn’t have infixes?
In Portuguese, you say “isso são outros quinhentos” (“that’s another five hundred”), apparently referring to an old joke. Before leaving the country to look for work in the capital city, a man gave the town’s priest five hundred contos de réis (old currency) for him to keep. The townspeople didn’t hear from that man again for many years. One day, he returned home and asked for his money back. But the poor preist had spent it on his church and claimed he didn’t remember about any money. A discussion ensued. Then a colonel graciously decided to help out the priest, and said – “it was to me you left the money”. But the sharp man replied – “wait, those are a different five hundred”
I am surprised no one mentioned “a FINE kettle of fish”. In the US this is a somewhat common expression. I believe it may have originated with the comedy team of Abbot and Costello or maybe the 3 Stooges, something like that.
In Romanian we say ” Altă gâscă în altă traistă.” (Another goose in another bag.) or “Asta e altă poveste” (This is another story.).