The bird in the clock (6)
I believe the answer is:
cuckoo
'the bird in the clock' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for cuckoo that I've seen before include "sound? Hardly!" , "No home bird, this" , "It lays eggs in another's 15 across" , "Onomatopoeic bird" , "nuts" .)