A transgression, initially shunning one and all, shows stupidity (9)
I believe the answer is:
asininity
'stupidity' is the definition.
(I've seen this before)
'a transgression initially shunning one and all' is the wordplay.
I cannot really see how this works, but
'a' is present in the answer.
'transgression' could be 'sin' (sin is a kind of transgression) and 'sin' is found in the answer.
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is present in the answer.
This explanation may well be incorrect...
'shows' is the link.
Can you help me to learn more?
(Other definitions for asininity that I've seen before include "Foolishness as of donkey" , "Extreme foolishness" , "Idiocy" , "Stupidity" .)