octobass
/ˌɒktə(ʊ)ˈbeɪs/Music. Now historical
noun
A very large instrument of the viol family, having three strings which were stopped by keys worked by the fingers and feet.
Origin
Late 19th century; earliest use found in Edward H. Knight (1824–1883), patent lawyer and expert in mechanics. From octo- + bass, after French octobasse.