The most common and most likely answer to this crossword clue is the 5 plus 3 letter word OPERA HAT
I've seen this crossword clue in The Daily Telegraph
O
P
E
R
A
H
A
T
More clues leading to the result OPERA HAT
- Atop her a strange item of headgear
- Artist wearing a top he designed, and a gibus
- A part he built under head of organisation that’s designed to collapse
- Topper, old and jaunty, covers topless 13
- Surgery on time, I’m not sure I’ve got it – I collapse in theatre
- Lid that collapses partly caught a hare poacher from behind
- I’m not sure I see through plump theatregoer’s attire
- Aretha, desperate, is after work that may be contracted in the theatre
- Hear a pot is broken in Glyndebourne feature?
- So that’s your game … wearing old, jaunty headgear!
Buddy explains!

The straight part
We know that "Glyndebourne feature" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case glyndebourne feature = opera hat.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.