For musicians or fabulous bard (not Norse) (5)

I believe the answer is:
ossia
This might be a double definition.
'for musicians' is the first definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'fabulous bard not norse' is the second definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.
Can you help me to learn more?
(Other definitions for ossia that I've seen before include "or Italian" , "(In musical scores) or" , "Indication of an alternative in music" , "musical alternative" , "Alternative notes" .)
