I always thought of this word as being British, however, I can only find it on dictionary.com. It does not appear in the OED. Can anyone shed any light on its origins?

Thanks,

Rousépeteur

Is it Canadian English for "WELCOME BACK!", by any chance? I hope that this forecasts an improvement in the chances of you fronting up for the foreseeable future.

By golly, bless my brolly, Rousepeteur posting again! Oh, happy day!
parapluie, gamp, umbrella! You're an extra welcome fella!
Parasol, that's not all! No parachute? Don't try a bumbershoot!
Here's what Quinion said:
http://www.quinion.com/words/qa/qa-bum2.htm

Tu est rousé maintenant, mon ami? C'est tout la même à moi.
Bienvenue! Je suis enchanté pour te voir encore! Oh--tu as une question!
Uh-oh--you might not like this, but here's a quote from the Word Detective:
While "bumbershoot" may sound exotic, its origin is remarkably straightforward: it's just a frivolous combination of the "umb" of "umbrella" and the "chute" of "parachute," which umbrellas vaguely resemble, after all. Although "bumbershoot" sounds to many people like an eccentric English, almost Tolkien-esque invention, it's actually an American coinage and the term is generally unknown in Britain. Today "bumbershoot" tends to be used, if at all, in cutesy weather reports ("So take the bumbershoot, all the way from Texas to the Great Lakes," CBS This Morning, 1992).
http://www.word-detective.com/112402.html#bumbershoot

>the "umb" of "umbrella"

one is tempted to say, "the 'umbr-' of umbrella." (as does M-W)

Let us not take umbrage over absemce of an r- .

It's always good to see the poetic side of Dr Bill erupt.

Hey, Rouspeteur, welcome back to the asylum.

*hehheh*
You thought you could escape us, mon amie. Mais non![twirling my imaginary, luxurious moustaches-e]