An insect for example, not very bright, going backwards (5)
I believe the answer is:
midge
'an insect' is the definition.
(midge is a kind of insect)
'example not very bright going backwards' is the wordplay.
'example' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'not very bright' becomes 'dim' (I've seen this before).
'going backwards' says the letters should be written backwards.
'eg'+'dim'='egdim'
'egdim' reversed gives 'MIDGE'.
'for' acts as a link.
(Other definitions for midge that I've seen before include "Two-winged fly" , "Small swarming biting insect" , "Gnat" , "Small, gnat-like fly" , "Tiny swarming insect" .)