Making pencil lead may give you quiet rheumatic pain (8)
I believe the answer is:
plumbago
'making pencil lead may give you quiet' is the definition.
I can't tell whether this definition defines the answer.
'rheumatic pain' is the wordplay.
'rheumatic' becomes 'p' (I can't explain this - if you can you should give a lot more credence to this answer).
'pain' becomes 'lumbago' (lumbago is a kind of pain).
'p'+'lumbago'='PLUMBAGO'
Can you help me to learn more?
(Other definitions for plumbago that I've seen before include "lead" , "Evergreen shrub" , "Plant type that includes sea pinks" , "Leadwort" , "Blue-flowered plant" .)