The term "pigeonhole" has multiple meanings. Originally, pigeonholes referred to small recesses where domestic pigeons nested. However, the term was later adopted to refer to small compartments built into desks and other furniture, because these compartments resembled the pigeons' nesting holes.
Pigeonholes were first used in the Middle Ages, when pigeons were domesticated and raised for their meat. Openings were created in walls or in pigeon cotes to provide the birds with a place to nest.
By 1789, the term "pigeonhole" was used to describe compartments in offices and writing cabinets because of their resemblance to a pigeon cote. These compartments were used to leave messages and to sort and file documents.
The term pigeonhole is also used as a verb meaning to assign someone or something to a particular class or category, especially in an overly rigid or exclusive manner. It can also refer to putting something aside for future consideration.