Fly jet carrying duke east (5)
I believe the answer is:
midge
'fly' is the definition.
(I've seen this before)
'jet carrying duke east' is the wordplay.
'jet' becomes 'mig'.
'carrying' is an insertion indicator.
'duke' becomes 'd'.
'east' becomes 'e' ('E' can be a synonym of 'east').
'mig' going around 'd' is 'midg'.
'midg'+'e'='MIDGE'
(Other definitions for midge that I've seen before include "Two-winged fly" , "Gnat" , "Small, gnat-like fly" , "A small biting gnat-like insect" , "Tiny swarming insect" .)