No rest in Wall Street for one holding onto the cash (6)
I believe the answer is:
wallet
'onto the cash' is the definition.
I can't tell whether this definition defines the answer.
'no rest in wall street for one' is the wordplay.
'no rest in' becomes 'wall' (I can't justify this - if you can you should believe this answer much more).
'wall' says to hollow out the word (remove centre letters) (I've seen 'walls of' mean this (only the edge letters remain)).
'street for one' becomes 'environment' (street is a kind of environment).
'environment' with its centre removed is 'et'.
'wall'+'et'='WALLET'
'holding' is the link.
Can you help me to learn more?
(Other definitions for wallet that I've seen before include "Money holder" , "Purse for notes" , "Pocket-size case" , "A man's pocketbpook" , "Shepherdess of rhyme" .)