In Medieval times (the actually time period, not the entertainment location) pigeons were kept as domestic birds for their meat. The pigeonhole referred to the openings in the wall or a hole in a specially made box for pigeons to live in.
By the late 18th century, the arrangement of compartments in writing cabinets and offices that were used to sort and file documents became known as pigeonholes for their resemblance to the old pigeon compartments.
By the 19th century, the term changed to refer to something that you would put aside to come back to later or to classify information.
If you feel that you are being pigeonholed at work just be thankful that your boss doesn’t plan to eat you like the poor pigeon.
Thank you Lauren for suggesting this word.