Flightless bird met at first in Brussels? (3)
I believe the answer is:
emu
'flightless bird' is the definition.
(emu is a kind of flightless bird)
'met at first in brussels?' is the wordplay.
'at first' suggests taking the first letters.
'in' means one lot of letters goes inside another.
'brussels?' becomes 'EU' (European Parliament is based in Brussels).
The initial letter of 'met' is 'm'.
'm' inserted inside 'eu' is 'EMU'.
(Other definitions for emu that I've seen before include "Australian non-flyer" , "Aussie runner" , "one offering challenge to Hull?" , "Parky's nemesis" , "it'll never fly!" .)