He contributes to the liquid assets of a bank (5,5)
I believe the answer is:
blood donor
'he contributes to' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'liquid assets of a bank' is the wordplay.
'liquid' becomes 'blood' (I have seen 'Red liquid ' mean 'blood' so perhaps 'liquid' could also mean 'blood').
'assets of a bank' becomes 'donor' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'blood'+'donor'='BLOOD-DONOR'
'the' is the link.
Can you help me to learn more?
(Other definitions for blood donor that I've seen before include "Enabler of transfusion" , "One giving to NHS" , "whose contribution is vital" .)