Dictionary.com has several definitions as a noun, including an open compartment, hole or recess. However, it is other use I had in mind. The term is used to describe what others think of an individual’s class or status, and it usually is used in a critical manner. (“He was pigeonholed as one of the kids who won’t behave.”) It also is used to describe something that has been set aside for the present, probably with the intention of ignoring it. (“The boss pigeonholed my idea.”) Wikipedia describes the origin was a mathematical term developed in the 1800’s. The example given is there has to be two pigeons in at least one compartment if there are 10 pigeons and 9 compartments. The idea of pigeons in compartments then evolved into catagorizing people and putting suggestions into slots to be forgotten.