Diligence demonstrated by essay on Asian river (8)
I believe the answer is:
industry
'diligence' is the definition.
(I know that diligence can be written as industry)
'essay on asian river' is the wordplay.
'essay' becomes 'try' (synonyms).
'on' says to put letters next to each other.
'asian river' becomes 'indus' (the Indus is an Asian river).
'try' put after 'indus' is 'INDUSTRY'.
'demonstrated by' is the link.
(Other definitions for industry that I've seen before include "Business" , "Diligence" , "Commercial, manufacturing enterprise" , "The manufacture or production of goods" , "Hard work" .)