Busman:
British -
bus driver
Holiday: British - day off, vacation
A
busman's holiday is a
vacation spent doing the same thing you do at work. For example, many E2
noders may have spent a day off from the
tech support farm fixing a friend's computer.
The origins of the phrase are unclear. The most
prosaic hypothesis is that a busman spends all day on a bus, and then when she decides to take a day off and enjoy the
countryside -- has to get back on a bus.
Another explanation
purportedly dates back to the 1800s, when buses were
horse-drawn carriages. The drivers were said to be so
dedicated that when they had a day off, they'd ride as passengers on their route to make sure that the
substitute wasn't abusing their animals or hassling their riders.
A third story suggests that the phrase actually descends from the
archaic slang buzz, to
pickpocket. A
buzzman always had her eyes open for a likely
mark, and so was at work even when on holiday.
sources:
http://www.word-detective.com/back-b.html
http://www.wordorigins.org/wordorb.htm
http://www.dictionary.com/cgi-bin/dict.pl?term=arab