Machinist joining this business involved in organic chemistry (7)
I believe the answer is:
grocery
'machinist joining this business involved in organic chemistry' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
This is all the clue.
Can you help me to learn more?
(Other definitions for grocery that I've seen before include "Shop selling foodstuffs" , "Food shop" , "Kind of shop" , "Type of food store" , "Shop for footstuffs" .)