Unfortunate target - rebel organisation (11)
I believe the answer is:
regrettable
'unfortunate' is the definition.
(similar in meaning)
'target rebel organisation' is the wordplay.
'organisation' indicates anagramming the letters.
'target'+'rebel'='targetrebel'
'targetrebel' is an anagram of 'REGRETTABLE'.
(Other definitions for regrettable that I've seen before include "Undesirable" , "ill-advised" , "Unfortunate" .)