A rain-napper is an umbrella. The name tells you exactly what it does: it naps — catches — the rain before the rain can catch you.

J. Redding Ware put it in Passing English of the Victorian Era (1909) as street slang and explained it in a line: Umbrella — because it catches the rain. From 'knap' — to catch quickly. That nap — to snatch — is the same old slang verb that survives in kidnap, thieves' cant of the 1680s for stealing children.

The word shows up on lists of Victorian slang, and it earned its place: John Camden Hotten's slang dictionaries carry it from 1859 onwards, and the 1874 edition has it plainly — Rain napper, an umbrella. But it was older than Victoria's reign.

Green's Dictionary of Slang finds it in 1821, in W. T. Moncrieff's Tom and Jerry, the stage version of Pierce Egan's Life in London and an outstanding hit — the first play, by one account, to run for 100 performances: Aye, put down the rain napper, Doctor, the shower is over now. So the word was already being spoken to London audiences sixteen years before Victoria came to the throne.

That is a common pattern with these lists. A great deal of what gets called Victorian slang was Regency slang that lasted — it is Victorian because Victorian dictionaries wrote it down, not because Victorians made it up.

The rain-napper outlasted the Victorians, too, at least on paper: an Australian slang dictionary still listed it in 1895, and Ware in 1909. It deserves another go. Umbrella is a perfectly good word, but it has never once sounded like it was fighting the weather.