Medieval forerunner of chemistry (7)
I believe the answer is:
alchemy
'medieval forerunner of chemistry' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for alchemy that I've seen before include "Search for gold and philosopher's stone" , "Medieval chemistry trying to change base metal to gold" , "Medieval activity to turn base metal into gold" , "Philosopher's Stone its object" , "Attempt at transformation" .)