Bolster painkiller, say, before eruption of pain (6)
I believe the answer is:
pillow
'bolster painkiller' is the definition.
'pillow' can be an answer for 'bolster' (I've seen this in another clue). I'm not sure about the 'painkiller' bit.
'before eruption of pain' is the wordplay.
'before' says to put letters next to each other.
'eruption of' becomes 'ow' (I can't explain this - if you can you should believe this answer much more).
'pain' becomes 'pill' (I've seen this in another clue).
'ow' put after 'pill' is 'PILLOW'.
'say' is the link.
Can you help me to learn more?
(Other definitions for pillow that I've seen before include "Sleeper's cushion" , "Soft place for the head" , "Item of bedding" , "Rest for the weary head" , "Cushion for head" .)