Possible association of his fans, all Tories? (6)
I believe the answer is:
monday
'association of his fans all tories?' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'possible' is the wordplay.
I cannot really understand how this works, but
'possible' could be 'on' ('not on' can mean unacceptable or not possible) and 'on' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for monday that I've seen before include "Part of the week" , "Week day" , "Dynamo (anag.)" , "First weekday" , "Start of the working week" .)