Blue boy? (5)
I believe the answer is:
peter
This might be a double definition.
'blue' is the first definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'boy?' is the second definition.
Can you help me to learn more?
(Other definitions for peter that I've seen before include "Rock-like apostle" , "and 16: Actor who played Hercule Poirot" , "Play high card before low" , "Fellow < safe" , "Leader of the Apostles" .)