It may pop out for an hour (6)
I believe the answer is:
cuckoo
This could be a double definition.
'it may pop out' is the first definition.
The definition suggests a singular noun which matches the answer. I also know that 'pop out' relates to this answer.
'an hour' is the second definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for cuckoo that I've seen before include "One calling on the hour" , "Bird which lays eggs in anothers nest" , "Unwelcome bird in the nest" , "Hourly you might hear this" , "Bats" .)