Musician with a bag under his arm (5)
I believe the answer is:
piper
'musician' is the definition.
(someone playing the bagpipes)
'a bag under his arm' is the wordplay.
I cannot quite see how this works, but
'a' could be 'per' (eg 'one a day' means 'one per day') and 'per' is found in the answer.
The remaining letters 'pi' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'with' is the link.
Can you help me to learn more?
(Other definitions for piper that I've seen before include "eg Flautist" , "English painter and stained glass designer, d. 1992" , "Instrumentalist, solo or military" , "One plays" , "Musician (who gets paid?)" .)