button

1. A type of round mechanical key that is used to change pitch on certain instruments. These include accordion, bandoneon, concertina, and Handäoline.

 

2. A name for the small pin that is at the end of a violin or similar insrtument that holds the tailpiece and allows tension to be put onto the strings.

 

3. A small semicircular extension on the back of a violin or similar insrtument that allows the back to be connected to the neck. This can provide additional stability for the neck.