Mainly, clothes of Parisian free of pretence (8)
I believe the answer is:
modestly
'free of pretence' is the definition.
Both the answer and definition are adverbs. Perhaps they are linked in a way I don't understand?
'mainly clothes of parisian' is the wordplay.
'mainly' becomes 'mostly' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'clothes' indicates putting letters inside (some letters clothe or cover others).
'of parisian' becomes 'de' ('of' in French).
'mostly' going around 'de' is 'MODESTLY'.
Can you help me to learn more?
(Other definitions for modestly that I've seen before include "In unassuming manner" , "In demure fashion" , "Unassumingly" , "without boasting" , "in low-key fashion" .)