Subject, universal form of gambling, not able to be discussed (3,6)
I believe the answer is:
sub judice
'subject' is the definition.
Both the answer and definition are adjectives. Perhaps there's a link between them I don't understand?
'universal form of gambling not able to be discussed' is the wordplay.
I cannot really see how this works, but
'universal' could be 'u' (film certificate) and 'u' is located in the answer.
'form' could be 'ice' (I have seen 'Form of water ' mean 'ice' so perhaps 'form' could also mean 'ice') and 'ice' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for sub judice that I've seen before include "Under consideration by court - don't comment" , "Under consideration by the courts - don't comment on it" , "Still before court" .)