Funny stories in an unsubstantiated statement (9)
I believe the answer is:
assertion
'unsubstantiated statement' is the definition.
'assertion' can be an answer for 'statement' (assertion is a kind of statement). I'm unsure of the 'unsubstantiated' bit.
'funny stories in an' is the wordplay.
'funny' is an anagram indicator.
'in' is an insertion indicator.
'stories' anagrammed gives 'ssertio'.
'ssertio' inserted into 'an' is 'ASSERTION'.
Can you help me to learn more?
(Other definitions for assertion that I've seen before include "Emphatic declaration" , "Claim" , "Confident statement of fact" , "Notarises (anag)" , "Confident declaration" .)