From the philologist's point of view:
The original instrument is the viola; in Italian there are som suffixes to determinate size:
Smaller than the original: Violina (m = -ino)
Bigger: Violone
A liitle bit smaller than the bigger, but bigger still than the original: Violoncello
So we have the entire family with soprano=violina, alto=viola, tenore=violoncello, and basso=violone.

Wilfried