Idea impracticable, I gathered (6)
I believe the answer is:
notion
'idea' is the definition.
(I know that notion is a type of idea)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for notion that I've seen before include "Idea or fancy" , "Vague impression" , "A vague and possibly incorrect opinion" , "Vague or whimsical idea" , "Concept, belief" .)