Bass violin is the modern term for various 16th- and 17th-century bass instruments of the violin (i.e. viola da braccio) family. They were the direct ancestor of the modern cello. Bass violins were usually somewhat larger than the modern cello, but tuned to the same nominal pitches or sometimes one step lower. Contemporaneous names for these instruments include "basso de viola da braccio," "basso da braccio," or the generic term "violone," which simply meant "large fiddle." The instrument differed from the violone of the viol, or "viola da gamba" family in that like the other violins it had at first three, and later usually four strings, as opposed to five, six, or seven strings, it was tuned in fifths, and it had no frets. With its F-holes and stylized C-bouts it also more closely resembled the viola da braccio.
The name "bass violin" is also sometimes used for the double bass.
Occasionally, historians have used the term "bass violin" to refer to other various instruments of the violin family that were larger than the alto violin or viola, such as the tenor violin. This use can be synonymous with "harmony violin."
After the 1950s, the term "bass violin" sometimes referred to a bass instrument of the violin octet.