Factory put underground? (5)
I believe the answer is:
plant
This could be a double definition.
'factory' is the first definition.
(a manufacturing plant)
'put underground?' is the second definition.
'plant' can be an answer for 'put' (planting is a kind of putting). I am not certain of the 'underground?' bit.
Can you help me to learn more?
(Other definitions for plant that I've seen before include "Factory; establish" , "Machinery; spy" , "Member of vegetable kingdom" , "Factory; organism" , "Vegetable organism" .)