Newly formed unit resented being unconcerned (12)
I believe the answer is:
uninterested
'unconcerned' is the definition.
(thesaurus)
'newly formed unit resented' is the wordplay.
'newly formed' indicates anagramming the letters.
'unit'+'resented'='unitresented'
'unitresented' anagrammed gives 'UNINTERESTED'.
'being' is the link.
(Other definitions for uninterested that I've seen before include "Apathetic" , "Not concerned" , "Bored" , "indifferent" .)