One caring about unfamiliarity (9)
I believe the answer is:
ignorance
'unfamiliarity' is the definition.
(thesaurus)
'one caring about' is the wordplay.
'about' indicates anagramming the letters.
'one'+'caring'='onecaring'
'onecaring' is an anagram of 'IGNORANCE'.
(Other definitions for ignorance that I've seen before include "Lack of knowledge" , "may be considered bliss" , "Lack of education" , "Being in the dark" , "Stupidity" .)