Advantage of entering river-flooded mine (6)
I believe the answer is:
profit
'advantage' is the definition.
(I know that profit is a type of advantage)
'entering river-flooded mine' is the wordplay.
'entering' is an insertion indicator.
'river' becomes 'r' (abbreviation).
'flooded' becomes 'of' (I can't explain this - if you can you should believe this answer much more).
'mine' becomes 'pit' (down the pit).
'r'+'of'='rof'
'rof' going inside 'pit' is 'PROFIT'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for profit that I've seen before include "Clean up" , "Advantage, benefit" , "It's gained on a transaction" , "Surplus earnings" , "Gain, return on investment" .)