The etymology of the phrase “it's raining cats and dogs”

Question

I was wondering about the phrase it's raining cats and dogs; I've heard two versions of the meaning of the phrase and I was wondering which one was correct or wrong altogether.

The first: with 16th century European peasant homes frequently being thatched, animals seeking shelter from the elements would fall out during heavy rains.

The second: that drainage in 17th century Europe was typically poor so they would, during heavy rains, disgorge any of the animal corpses that had accumulated in them.

Answer 1

There are a few theories, that's for sure. But the bottom line is, the etymology is unknown. I won't leave you without these pointers, though:

• The Phrase Finder:

  This is an interesting phrase in that, although there's no definitive origin, there is a likely derivation. [...] The fact that [Jonathan] Swift had alluded to the streets flowing with dead cats and dogs some years earlier and [in 1738] used 'rain cats and dogs' explicitly is good evidence that poor sanitation was the source of the phrase as we now use it.

• Wikipedia:

  The English idiom "it is raining cats and dogs", used to describe an especially heavy rain, is of unknown etymology [...] There may not be a logical explanation; the phrase may have been used just for its nonsensical humor value[.]

Answer 2

Phrase to rain cats and dogs is attested from 1738 (variation rain dogs and polecats is from 1652), of unknown origin, despite intense speculation.

[Reference: Etymonline.com]

Some other theories:

• The archaic French catdoupe is a waterfall or cataract, lightning and thunder sounds like that of a cat/dog fight, cats had a big influence on the weather, and the sky dog Odin was attended to by wolves according to Norse Mythology.
• Another theory is that in old England, they had hay roofs on their houses and the cats and dogs would sleep on the roof. When it rained, the roofs got slippery and the cats and dogs would slide off of the roofs. There for it was "Raining Cats and Dogs".
• "Rain Cats and Dogs" stems from the Norse Mythology. Cats were believed to represent the wind and dogs represented rain. Different animals represented different weather and natural phenomenon.