Diapason stop is a term commonly used in the world of music and refers to a pipe organ stop that produces a full and rich tone. While diapason stop is a widely recognized term within this realm, there are also several synonyms that can be used interchangeably. These include the term Principal-stop, which is a common name for the diapason stop. Other common synonyms include the Open Diapason stop, the Grand Diapason, or simply the Diapason. The use of these synonyms may vary depending on the region or specific context, but all of them refer to the same pipe organ stop that produces a bright and full sound.