Grand little fellow, this flier? (4)
I believe the answer is:
gnat
'this flier?' is the definition.
(I have seen 'annoying flier' mean 'gnat' so perhaps 'flier' could also mean 'gnat')
'grand little fellow' is the wordplay.
'grand' becomes 'g' (G is short for grand as in a thousand).
'little fellow' becomes 'nat' (I am not sure about this - if you are sure you should believe this answer much more).
'g'+'nat'='GNAT'
Can you help me to learn more?
(Other definitions for gnat that I've seen before include "Stinging insect" , "Two-winged fly" , "Small biting fly" , "small irritant" , "Woodland area" .)