Nope, it's a valid word alright. I came across it in a P.G.Wodehouse -
The Manoeuvres of Charteris.

http://www.readbookonline.net/readOnLine/1936/ ( just search for
berrain ). Great story too, if you like PGW.

It goes something like this:

'Why on earth are you slacking in here on this ripping afternoon?'
'Slacking!' said Charteris. 'I like that. I'm doing berrain work,
Babe.
I'm writing an article on masters and their customs, which will cause
a profound sensation in the Common Room. At least it would, if they
ever saw it, but they won't. Or I hope they won't for their sake _and_
mine. So run away, my precious Babe, and don't disturb your uncle when
he's busy.'

Charteris isn't Irish and i haven't come across a dict that had that
word and i've always wondered.. though the sense does come across.