To start trouble - for whatever cause - is very bad (7)
I believe the answer is:
treason
'very bad' is the definition.
The definition and answer can be both human attributes as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'to start trouble for whatever cause' is the wordplay.
I cannot quite see how this works, but
'cause' could be 'reason' (I've seen this before) and 'reason' is found in the answer.
A single letter 't' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'is' is the link.
Can you help me to learn more?
(Other definitions for treason that I've seen before include "One rats (anag)" , "One's art? (anag)" , "Offence against state" , "subversion" , "Mutiny" .)