Splendour, impressiveness (8)
I believe the answer is:
grandeur
I believe this clue is a double definition.
'splendour' is the first definition.
(synonyms)
'impressiveness' is the second definition.
(I've seen this before)
(Other definitions for grandeur that I've seen before include "Majesty (God's, Hopkins)" , "Pomp" , "Impressive splendour" , "Majesty - eminence" , "Nobility, dignity" .)