E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A temporary prison. Galignani says: In the time of Louis XI. the Salle-de-Perdus was so full of turbulent clerks and students that the bailiff of the palace shut many up in the lower room of the conciergerie (prison) while the courts were sitting; but as they were guilty of no punishable offence, he allowed them a violin to wile away the tedium of their temporary captivity.
M. Génin says the seven penitential psalms were called in the Middle Ages the psalterion, and to put one to penance was in French expressed by mettre au psalterion. As the psaltery was an instrument of music, some witty Frenchman changed psalterion to violon, and in lieu of mettre au psalterion wrote mettre au violon.