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. Nachthorn [noun] - a flue stop with several different types. In the very early Dutch organ it was a type of Cornet. From about the time of Praetorius on, it was a stopped flute with a highly developed twelfth, between a Gedeckt and a Quintaton. In later periods it can also be found as a wide-scale (but not loud) open flute. Nebenwerk Neo-Classic Non-Return Valve