A Dictionary of Music and Musicians/Solo Stop
SOLO STOP, (1) A stop or register of a solo organ or fourth manual. (2) Any stop which can be used as a solo—that is, in single notes, e.g. a clarinet on the choir organ; a cornopean, hautboy, or other reed on the swell organ; a clarabella or flute on either of the three manuals great, swell, or choir. The name Solo stop does not necessarily imply that full chords may not be used upon it. [See Solo Organ.]
[ J. S. ]