First recorded
in 1848, open and shut probably didn"t originate in a lawyer's office. A
good bet is that it had its origins in some card game, probably either poker or
faro. Simpler version of these games didn"t allow complicated betting but shut
the pot after it was opened and the ante was put in. The term could have passed
into general use from the card tables to take on the meaning of "easily decided
or immediately obvious," as in an open and shut case of murder.