Authentic clothing — grand and majestic (5)
I believe the answer is:
regal
'majestic' is the definition.
(synonyms)
'authentic clothing grand' is the wordplay.
'authentic' becomes 'real' (I've seen this before).
'clothing' is an insertion indicator (some letters cover up or clothe others).
'grand' becomes 'G' (G is short for ground as in a thousand).
'real' enclosing 'g' is 'REGAL'.
'and' acts as a link.
(Other definitions for regal that I've seen before include "Showing great dignity" , "King-like" , "Like a queen?" , "Magnificent, dignified" , "fit for the Queen" .)