'Outlook' is necessary, not as organised (7)
I believe the answer is:
scenery
'outlook' is the definition.
(thesaurus)
'necessary not as organised' is the wordplay.
'not' is a deletion indicator.
'organised' indicates anagramming the letters.
'necessary' with 'as' taken out is 'necesry'.
'necesry' anagrammed gives 'SCENERY'.
'is' is the link.
(Other definitions for scenery that I've seen before include "On-stage background" , "Landscape, view" , "Attractive landscape" , "episode" , "Theatrical set, backdrop" .)