Necklace ball (4)
I believe the answer is:
bead
'necklace ball' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for bead that I've seen before include "Element of rosary" , "Part of a necklace" , "A bit of the rosary" , "Bauble" , "Small round piece of glass" .)