This may mean hell if any sidled off (6,3)
I believe the answer is:
deadly sin
'this may mean hell' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'any sidled off' is the wordplay.
'off' indicates an anagram.
'any'+'sidled'='anysidled'
'anysidled' anagrammed gives 'DEADLY SIN'.
'if' acts as a link.
Can you help me to learn more?
(Other definitions for deadly sin that I've seen before include "Eg, lust or gluttony" , "a cause of damnation" , "Lethal lapse like pride, gluttony or envy" , "Eg, lust or pride" , "Anger, say" .)