The slenderness of Anne - not so round (8)
I believe the answer is:
leanness
'the slenderness' is the definition.
The definition and answer can be both human attributes as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'of anne not so round' is the wordplay.
'of' indicates anagramming the letters (the answer comes from or 'of' the letters).
'not so' becomes 'less' (eg 'not so big' means 'less big').
'round' means one lot of letters goes inside another.
'anne' is an anagram of 'eann'.
'eann' put inside 'less' is 'LEANNESS'.
Can you help me to learn more?
(Other definitions for leanness that I've seen before include "Thinness" , "thin" , "Lack of fat" .)