...or a design on a magnificent scale (9)
I believe the answer is:
grandiose
'on a magnificent scale' is the definition.
I can't tell whether this defines the answer.
'or a design' is the wordplay.
'or a design' can be anagrammed to 'GRANDIOSE'.
However, I'm unsure how the anagram is indicated.
Can you help me to learn more?
(Other definitions for grandiose that I've seen before include "Pretentiously imposing -- organised (anag)" , "I grade son as affectedly splendid" , "Bombastic" , "Impressive in style" , "Ridiculously impressive or imposing" .)