The most common and most likely answer to this crossword clue is the 11 letter word HEADDRESSES
I've seen this crossword clue in Financial Times
H
E
A
D
D
R
E
S
S
E
S
More clues leading to the result HEADDRESSES
Buddy explains!
The straight part
We know that "clothing at the highest level" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case clothing at the highest level = headdresses.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 HEADDRESSES mean?
HEADDRESSES noun- A decorative covering or ornament worn on the head.
- A hairdo.