Tail pinned to cuckoo (3,5)
I believe the answer is:
end point
'tail' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'pinned to cuckoo' is the wordplay.
'cuckoo' indicates anagramming the letters.
'pinned'+'to'='pinnedto'
'pinnedto' is an anagram of 'END POINT'.
Can you help me to learn more?
(Other definitions for end point that I've seen before include "stop appearing here?" , "Final stage of a process" .)