One new position for illustration (8)
I believe the answer is:
instance
'for illustration' is the definition.
(synonyms)
'one new position' is the wordplay.
'one' becomes 'i' (Roman numeral).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'position' becomes 'stance' (stance is a kind of position).
'i'+'n'+'stance'='INSTANCE'
(Other definitions for instance that I've seen before include "An insect (anag.)" , "A case or example of something" , "Cite as an example" , "Case - isn't acne (anag)" , "Canniest (anag) - occurrence" .)