Bad form, pinching inventor's first idea (6)
I believe the answer is:
notion
'idea' is the definition.
(I know that notion is a type of idea)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for notion that I've seen before include "Concept, belief" , "Vague understanding" , "Vague impression" , "Whimsical idea or small sewing article" , "Caprice" .)