Bass viol and Double-bass

Bass viol noun - Viol that is the bass member of the viol family with approximately the range of the cello.

Double-bass and bass viol are semantically related. In some cases you can replace phrase "Double-bass" with "Bass viol", this phrases are similar.

Double-bass adjective - Pitched an octave below normal bass instrumental or vocal range.

Bass viol and double-bass are semantically related. You can use "Bass viol" instead a noun phrase "Double-bass".