Awful building largely embodies design only occasionally used (7)
I believe the answer is:
heinous
'awful' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for heinous that I've seen before include "Execrable" , "Wicked (offence)" , "Appalling (crime)" , "Awful" , "Despicable" .)