Presently it could be a conspiracy theory – no question (4)
I believe the answer is:
anon
'presently' is the definition.
(synonyms)
'it could be a conspiracy theory no question' is the wordplay.
I cannot quite see how this works, but
'a' could be 'an' and 'an' is found in the answer.
'no' could be 'o' (resembles 0 - 'no' can mean 'zero') and 'o' is located in the answer.
A single letter 'n' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for anon that I've seen before include "Nameless - presently" , "Soon, precious stone" , "prolific author" , "Not identified by name" , "Soon, shortly (archaic)" .)