Having many factories on River Test (10)
I believe the answer is:
industrial
'having many factories' is the definition.
I can't tell whether this defines the answer.
'on river test' is the wordplay.
'on' says to put letters next to each other.
'river' becomes 'indus' (Indian river).
'test' becomes 'trial' (synonyms).
'indus' put next to 'trial' is 'INDUSTRIAL'.
Can you help me to learn more?
(Other definitions for industrial that I've seen before include "Type of action" , "plants may be so described" , "Like manufacturing" , "Inlaid rust (anag.)" , "Involved in manufacture" .)