Something growing in factory (5)
I believe the answer is:
plant
'factory' is the definition.
(a manufacturing plant)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for plant that I've seen before include "Growing organism - industrial buildings" , "Hide in order to be found" , "eg Flower" , "Put in the ground to grow" , "Factory; spy" .)