They are not particular in a manner of speaking (12)
I believe the answer is:
'they' is the definition.
Both the answer and definition are plural nouns.
Perhaps there's a link between them I don't understand?
'not particular in a manner of speaking' is the wordplay.
'not particular' becomes 'general' (I've seen this in another clue).
'in a manner of speaking' becomes 'ities' (I can't justify this - if you can you should give a lot more credence to this answer).
'are' acts as a link.
Can you help me to learn more?