Heading for precious choice of addresses (4,3,2,5)
I believe the answer is:
dear sir or madam
'heading' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.
'precious choice of addresses' is the wordplay.
I cannot really understand how this works, but
'precious' could be 'dear' (I've seen this before) and 'dear' is found in the answer.
'of' could be 'o' and 'o' is present in the answer.
This explanation may well be incorrect...
'for' acts as a link.
Can you help me to learn more?
(Another definition for dear sir or madam that I've seen is " Formal introduction".)