Detailed regalia intended to cloak common unimportance (14)
I believe the answer is:
insignificance
'unimportance' is the definition.
(I know that insignificance is a type of unimportance)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for insignificance that I've seen before include "The quality of trifles" , "Unimportance" .)