bass viol

/B AE1 S V AY0 AH0 L/
noun
  1. 1

    A fretted, bowed, stringed musical instrument from the viola da gamba family. It occupies the bass range and is the lowest instrument in the family. Similar to (but smaller than) a cello.

    My piano teacher also plays the bass viol.

Source: https://en.wiktionary.org/wiki/bass%20viol