Monsieur in European Union — one that won’t fly? (3)
I believe the answer is:
emu
'one that won't fly?' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'monsieur in european union' is the wordplay.
'monsieur' becomes 'm' (French abbreviation - like Mr for Mister).
'in' means one lot of letters goes inside another.
'european union' becomes 'eu'.
'm' inserted within 'eu' is 'EMU'.
Can you help me to learn more?
(Other definitions for emu that I've seen before include "it'll never fly!" , "Native Australian bird" , "Bird of tremulous kind" , "Ratite" , "Australian running bird." .)