Not one on view (6)
I believe the answer is:
notion
'view' is the definition.
(I know that notion is a type of view)
'not one on' is the wordplay.
'one' becomes 'i' (Roman numeral).
'not'+'i'+'on'='NOTION'
(Other definitions for notion that I've seen before include "clue" , "Vague idea or opinion" , "Concept, belief" , "desire" , "Whimsical idea or small sewing article" .)