Raining cats and dogs

The English idiom "it is raining cats and dogs", used to describe particularly heavy rain, is of unknown etymology and is not necessarily related to the raining animals phenomenon. The phrase (with "polecats" instead of "cats") has been used at least since the 17th century. A number of possible etymologies have been put forward to explain the phrase; for example: Drainage systems on buildings in 17th-century Europe were poor and may have disgorged their contents during heavy showers, including the corpses of any animals that had accumulated in them. This occurrence is documented in Jonathan Swift's 1710 poem "Description of a City Shower", in which he describes "Drowned puppies, stinking sprats, all drenched in mud,/Dead cats and turnip-tops come tumbling down the flood." "Cats and dogs" may be a corruption of the Greek word Katadoupoi, referring to the waterfalls on the Nile, possibly through the old French word catadupe ("waterfall").