One naturally separated from the rest of humanity (8)
I believe the answer is:
islander
'rest of humanity' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'one naturally separated' is the wordplay.
'one' becomes 'i' (Roman numeral).
'naturally separated' becomes 'slander' (I am not sure about this - if you are sure you should believe this answer much more).
'i'+'slander'='ISLANDER'
'from the' acts as a link.
Can you help me to learn more?
(Other definitions for islander that I've seen before include "Inhabitant of Skye, say" , "Eg, a Manxman" , "One living surrounded by water" , "Sicilian, e.g." , "E.g. Shetland inhabitant" .)