A question on the census for half the spies? (3)
I believe the answer is:
age
'a question on the census' is the definition.
I can't judge whether this definition defines the answer.
'half the spies?' is the wordplay.
'half' indicates taking half.
'the spies?' becomes 'agents' (spy is a kind of agent).
'agents' with half the letters taken is 'AGE'.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for age that I've seen before include "Long period" , "Years since birth" , "Time in years" , "Length of life" , "Epoch" .)