Neckline that may bring out a whistle (7)
I believe the answer is:
lanyard
'neckline that' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'bring out a whistle' is the wordplay.
'bring' becomes 'land' (synonyms).
'out' means to remove the last letter.
'a whistle' becomes 'yard' (I can't justify this - if you can you should give a lot more credence to this answer).
'land' with its last letter taken away is 'lan'.
'lan'+'yard'='LANYARD'
'may' acts as a link.
Can you help me to learn more?
(Other definitions for lanyard that I've seen before include "Ribbon or cord around neck" , "Part of rigging" , "Line for extending or fastening ship's rigging" , "Short rope used as a fastening" , "Nautical rope" .)