Notion or concept
I believe the answer is:
idea
This clue is a double definition.
'notion' is the first definition.
(I've seen this before)
'concept' is the second definition.
(I've seen this in another clue)
(Other definitions for idea that I've seen before include "Inkling" , "Product of the mind" , "It comes to mind" , "Suggestion" , "Proposal" .)