The piece between one's teeth? (3)
I believe the answer is:
bit
'the piece' is the definition.
('bit' can be a synonym of 'piece')
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for bit that I've seen before include "scrap" , "Part of 21 across" , "Snaffle - small piece" , "Took effect - fragment" , "Between horse's teeth, this loses control" .)