Identify a key part that needs watching (5)
I believe the answer is:
telly
'part that needs watching' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'identify a key' is the wordplay.
'identify' becomes 'tell' (telling is a kind of identifying).
'a key' becomes 'y' (I can't explain this - if you can you should give a lot more credence to this answer).
'tell'+'y'='TELLY'
Can you help me to learn more?
(Other definitions for telly that I've seen before include "cop in seventies" , "One of the media" , "Familiar name for TV" , "The goggle-box" , "Television" .)