Aide's unusual impression (4)
I believe the answer is:
'impression' is the definition.
(I've seen this in another clue)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for idea that I've seen before include "Inkling" , "intellectual product" , "Suggestion" , "Content of cognition" , "Notion in the mind" .)