It’s raining cats and dogs is an idiom which means it’s raining extremely heavily. The origin of the phrase raining cats and dogs is steeped in mystery. There are several theories, one being that the phrase raining cats and dogs references the mythologies of the Norse god Odin and English witches. Odin was depicted as traveling in storms with dogs and wolves, cats were well-known familiars of witches.
Another possible source of inspiration for the term raining cats and dogs is the filth of seventeenth century London. Stray animals lived and died untended. When streets became swollen with rain it is likely there were many dead dogs and cats floating in the flooded streets, giving the appearance of having rained cats and dogs. The oldest known use of this term occurred in 1651, in a collection of poems by Henry Vaughan in which he alludes to a roof that was secure against “dogs and cats rained in shower.” Jonathon Swift penned “I know Sir John will go, though he was sure it would rain cats and dogs” in A Complete Collection of Polite and Ingenious Conversation, in 1738.
Examples
It rained cats and dogs during the monsoon season. (The New Indian Express)
Those who were in Kampala will remember that Friday when it rained cats and dogs followed by floods and endless traffic jams all over the city. (The Observer)
“It’s rained cats and dogs since Saturday — 10, 11, up to 12 inches,” Brumant said. (The St. Croix Source)
“The first year, it rained cats and dogs and we still had about 5,000 attend,” she said. (The Columbus Ledger-Enquirer)
It rained cats and dogs during the first Batalla in St. Augustine, and the 50 or 60 of us who participated all laughed until our sides hurt. (The St. Augustine Record)