Underhand type of participating Stockholm banks (4)
I believe the answer is:
palm
This might be a double definition.
'underhand type' is the first definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe you can see a link between them that I don't see?
'of participating stockholm banks' is the second definition.
The definition suggests a singular noun which matches the answer.
Can you help me to learn more?
(Other definitions for palm that I've seen before include "Tree symbolising victory" , "that's inspected by a fortune-teller" , "Tropical tree; conceal" , "prize" , "Symbol of victory" .)