The most common and most likely answer to this crossword clue is the 8 letter word AIGRETTE
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More clues leading to the result AIGRETTE
Buddy explains!

The straight part
We know that "piece of jewellery" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case piece of jewellery = aigrette.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 AIGRETTE mean?
AIGRETTE noun- A feather or plume, or feather-shaped item, used as an adornment or ornament.
- The lesser white heron.
- The feathery crown of some seeds (such as the dandelion).