A boss set about getting banned substance (8)
I believe the answer is:
asbestos
'banned substance' is the definition.
'asbestos' can be an answer for 'substance' (asbestos is a kind of substance). I am not sure about the 'banned' bit.
'a boss set about' is the wordplay.
'about' is an anagram indicator.
'boss'+'set'='bossset'
'bossset' with letters rearranged gives 'sbestos'.
'a'+'sbestos'='ASBESTOS'
'getting' is the link.
Can you help me to learn more?
(Other definitions for asbestos that I've seen before include "retardant" , "Heat-resistant fibre" , "Old fire-retardant" , "Heat-resistant material" , "'Fireproof substance, dangerous to health (8)'" .)