One's enveloped by kind spirit (6)
I believe the answer is:
genius
'spirit' is the definition.
(thesaurus)
'one's enveloped by kind' is the wordplay.
'one' becomes 'i' (Roman numeral).
'enveloped by' indicates putting letters inside.
'kind' becomes 'genus' (genus is a kind of kind).
'i' placed inside 'genus' is 'GENIUS'.
(Other definitions for genius that I've seen before include "Huge mental ability" , "One has an extraordinary talent" , "Person with exceptional creative ability" , "A natural talent" , "Person of exceptional mental ability" .)