The most common and most likely answer to this crossword clue is the 7 letter word SAUTOIR
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More clues leading to the result SAUTOIR
Buddy explains!

The straight part
We know that "Necklace" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case necklace = sautoir.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 SAUTOIR mean?
SAUTOIR noun- A ribbon, chain, scarf, or the like, tied around the neck in such a manner that the ends cross over each other.
- A chain to which a pendant is attached, worn around the neck.