The only literal explanation for raining
cats and dogs is that during heavy rains in seventeenth-century England
some city streets became raging rivers of filth carrying many dead cats
and dogs. The first printed use of the phrase does date to the seventeenth
century, when English playwright Richard Brome wrote in The City Witt
(1652): "It shall rain dogs and polecats." His use of "polecats" certainly
suggests a less literal explanation, but no better theory has been
offered. Other conjectures are that the hyperbole comes from a Greek
saying, similar in sound, meaning "an unlikely occurrence," and that the
phrase derives from a rare French word, catadoupe ("a waterfall"), which
sound a little like cats and dogs. It could also be that the expression
was inspired by the fact that cats and dogs were closely associated with
the rain and wind in northern mythology, dogs often pictured as the
attendants of Odin, the storm god, and cats believed to cause storms.
Similar colloquial expressions include it's raining pitchforks, darning
needles, hammer handles, and chicken coops.