Silly sort of clock? (6)
I believe the answer is:
cuckoo
This clue might be a double definition.
'silly' is the first definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'sort of clock?' is the second definition.
Can you help me to learn more?
(Other definitions for cuckoo that I've seen before include "Slightly crazy -- bird" , "Bird with distinctive cry" , "Bird which lays eggs in others' nests" , "Bananas" , "slightly mad type" .)