Magnificent, imposing (5)
I believe the answer is:
grand
I believe this clue is a double definition.
'magnificent' is the first definition.
(I've seen this before)
'imposing' is the second definition.
(I know that imposing can be written as grand)
(Other definitions for grand that I've seen before include "Large and imposing" , "Splendid - piano" , "Stately - splendid" , "Magnificent, imposing" , "Piano; thousand pounds" .)