Profit that is invested by unknown land's banks (5)
I believe the answer is:
yield
'profit' is the definition.
(I've seen this before)
'invested by unknown land's banks' is the wordplay.
'invested' becomes 'ie' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'by' is a charade indicator (letters next to each other).
'unknown' becomes 'y' (algebra).
'banks' suggests removing the centre (the sides or banks of the word).
'land' with its middle removed is 'ld'.
'ie' after 'y' is 'yie'.
'yie'+'ld'='YIELD'
'that is' acts as a link.
Can you help me to learn more?
(Other definitions for yield that I've seen before include "Concede, give in" , "Succumb" , "Produce, generate" , "Bring forth" , "bow" .)