Posh clothes of the better class Yankee (6)
I believe the answer is:
finery
'posh clothes' is the definition.
'finery' can be an answer for 'clothes' (finery is a kind of clothes). I am not sure about the 'posh' bit.
'the better class yankee' is the wordplay.
I cannot quite understand how this works, but
'better' could be 'finer' (I've seen this in another clue) and 'finer' is found in the answer.
'yankee' could be 'y' (phonetic alphabet: alpha, bravo, charlie etc.) and 'y' is found in the answer.
This accounts for all the letters.
This may be the basis of clue (or it may be nonsense).
'of' is the link.
Can you help me to learn more?
(Other definitions for finery that I've seen before include "Ostentatious clothes" , "Regalia" , "smart clothes" , "Elaborate clothing, jewellery etc" , "Ostentatious clothing" .)