The sameness of unique characteristics (8)
I believe the answer is:
identity
This could be a double definition.
'the sameness' is the first definition.
(identity is a kind of sameness)
'unique characteristics' is the second definition.
'identity' can be an answer for 'characteristics' (I have seen 'Individual characteristics ' mean 'identity' so perhaps 'characteristics' could also mean 'identity'). I'm unsure of the 'unique' bit.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for identity that I've seen before include "Close affinity" , "Sameness; selfhood" , "sort of card" , "character" , "The question of who one is" .)