These pages comprise a dictionary of terms relating to the pipe organ. Please keep definitions to a few sentences, and do not include pictures or sound clips. When more space is needed for a term, a new page can be created for it.


Oberwerk [noun] - a traditional German name for one of the divisions of the organ. It might mean the keyboard above the main division, a division architecturally higher in the case, or sometimes it's the main division itself (instead of Hauptwerk).

Oboe [noun] - a reed stop of moderate power. It has been voiced in many ways, but is generally bright, not as loud as the Trumpet-type reeds, and not really imitative of its namesake. The stop which is designed to recreate the wind instrument is called the Orchestral Oboe. In the works of Franck, the Hautbois (Oboe) was commonly added to the foundations of the Récit as an ensemble stop.

Octave [noun] - A diapason stop sounding the first overtone, or the eighth pitch above the fundamental

Octave Coupler A device which causes the note one octave higher to be added when a key is depressed. There is also a sub-octave coupler which adds the note one octave lower. See also Unison Off.

Octavin [noun] In the style of Cavaillé-Coll, a harmonic flute stop at the 2' pitch level

Octopod [noun] - a somewhat derogatory colloquialism used to describe organs with few (if any) stops at any pitch other than 8', typically from the late 19th and early 20th centuries.

Offset Chest [noun] - a chest, usually smaller than the main chest of a division, on which stand large pipes that wouldn't fit on the main chest (sometimes because of their height).

Open [adjective] a pipe which is open at the end not resting on the windchest. Compare with Stopped.

Open Diapason [noun] - A stop exhibiting the characteristic sound of the organ, comprised of moderate-scale open metal cylindrical pipes. In British usage to distinguish from "Stopped Diapason" which is really a stopped flute.

Open Wood [noun] - A traditional pedal stop of the English-style 19th-20th century organ. It was a large-scale open wood rank which provided a strong, if not terribly clear, foundation to the pedal division. Usually a 16' stop, but sometimes found at 32', the pipes were full-length.

Orchestral [noun] a division containing orchestral stops (see Orchestral [adj.]).

Orchestral [adj.] a stop which is intended to closely imitate the sound of an orchestral instrument; for example: Orchestral Flute, Orchestral Trumpet, Orchestral Violin.

Organ [noun] - Today taken to mean the whole instrument, including the pipes, blower(s),console, and all connecting equipment. Traditionally, each keyboard and its pipes were spoken of as a separate organ, e.g. the "Swell Organ" as opposed to the "Great Organ".

Organo Pleno - Latin for "full organ", and may mean a variety of effects depending on the type of music and the period in which it was written. In 18th century north European music, it could mean something like full principal chorus to mixtures (with or without reeds) on the Great and the same plus a 16' reed in the pedal. By the time of Reger and Karg-Elert, it was more like all the stops that could reasonably be used, with all divisions coupled together.

Orgelbüchlein [noun]- A book of 46 short chorale preludes for the church's year written by J S Bach for the use and intruction of parish organists. This is a youthful work, dating from about 1714, but shows a complete command of the form, and is a masterpiece of tone-painting.

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