Durability of novelty gift not half bad (9)
I believe the answer is:
longevity
'durability' is the definition.
(thesaurus)
'novelty gift not half bad' is the wordplay.
'not half' suggests halving the letters.
'bad' is an anagram indicator.
'gift' halved is 'gi'.
'novelty'+'gi'='noveltygi'
'noveltygi' anagrammed gives 'LONGEVITY'.
'of' is the link.
(Other definitions for longevity that I've seen before include "Tiny glove (anag.)" , "Great length of life" , "endurance" , ""Length of days"" , "Duration of service" .)