Interesting Origin of phrases – Its raining cats and dogs

Its raining cats and dogs

Meaning

It is raining unusually or unbelievably.

Origin

Houses in the 1500s had thatched roofs-thick straw-piled high, with no wood underneath. It was the only place for animals to get warm, so all the cats and other small animals (mice, bugs) lived in the roof. When it rained it became slippery and sometimes the animals would slip and fall off the roof. Hence the saying ... "It's raining cats and dogs."

PS:

This is one of the oldest phrases so much so that it has a biblical reference to it.  It seems that cats were at one time thought to have influence over storms, especially by sailors, and that dogs were symbols of storms, often accompanying images and descriptions of the Norse storm god  - Odin. So when some particularly violent tempest appeared, people suggested it was caused by cats (bringing the rain) and dogs (the wind).