Cuckoo nest had mouthpiece (7)
I believe the answer is:
handset
'mouthpiece' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's a link between them I don't understand?
'cuckoo nest had' is the wordplay.
'cuckoo' indicates an anagram (I've seen this in other clues).
'nest'+'had'='nesthad'
'nesthad' with letters rearranged gives 'HANDSET'.
Can you help me to learn more?
(Other definitions for handset that I've seen before include "part of phone" , "Phone receiver" , "controller" , "Part of a telephone" , "Shed tan (anag.)" .)