Narrow part of a bottle (4)
I believe the answer is:
neck
'narrow part of a bottle' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for neck that I've seen before include "One may get it in it!" , "A hard one shows some nerve" , "and what is at the bottom of it" , "Isthmus; impudence (sl.)" , "Kiss amorously" .)