Wherein, in short, chemists labour (3)
I believe the answer is:
lab
'labour' is the definition.
(abbreviation)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for lab that I've seen before include "In brief, a room for scientific experiments" , "Research workroom" , "SECOND PART OF 15" , "retriever" , "Room for scientist" .)