Impressive, splendid (5)
I believe the answer is:
grand
I believe this clue is a double definition.
'impressive' is the first definition.
(similar in meaning)
'splendid' is the second definition.
(both can mean impressive)
(Other definitions for grand that I've seen before include "GBP1,000" , "PS1000 (sl.)" , "Marvellous" , "Splendid - piano" , "great distinction" .)