Aide made odd impression (4)
I believe the answer is:
idea
'impression' is the definition.
(I've seen this in another clue)
'aide made odd' is the wordplay.
'made odd' indicates an anagram (an unusual or odd ordering of the letters).
'aide' is an anagram of 'IDEA'.
(Other definitions for idea that I've seen before include "Product of the mind" , "Mental impression" , "Notion in the mind" , "Fancy" , "Light bulb above head" .)