The most common and most likely answer to this crossword clue is the 4 plus 5 letter word GOLD PLATE
I've seen this crossword clue in The Sunday Telegraph
G
O
L
D
P
L
A
T
E
Buddy explains!

The straight part
We know that "Gilt" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case gilt = gold plate.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GOLD PLATE mean?
GOLD PLATE verb- To apply gold plate to an object, to plate with gold.
- (of projects) To incorporate costly or otherwise excessive features or refinements unnecessarily, to overengineer.
- (of laws, regulations, etc) To embellish, to extend beyond its intended scope, especially so as to become stifling, or rigid and inflexible.