Disguise nature of feminine opinion (6)
I believe the answer is:
belief
'opinion' is the definition.
(an opinion is a personal belief)
'disguise nature of feminine' is the wordplay.
I cannot really understand how this works, but
'disguise' could be 'belie' (I've seen this in another clue) and 'belie' is found in the answer.
'feminine' could be 'f' (abbreviation listed in Chambers) and 'f' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for belief that I've seen before include "Persuasion" , "Faith, credence" , "Trust, faith (6)" , "Principle accepted without proof" , "Faith; confidence" .)