Imposing (5)
I believe the answer is:
grand
'imposing' is the definition.
(I know that imposing can be written as grand)
This is all the clue.
(Other definitions for grand that I've seen before include "Magnificent, imposing" , "A slangy PS1,000" , "Splendid - piano" , "Designed to impress" , "GBP1,000" .)