Group lunacy (7)
I believe the answer is:
madness
This could be a double definition.
'group' is the first definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'lunacy' is the second definition.
(synonyms)
Can you help me to learn more?
(Other definitions for madness that I've seen before include "great anger" , "hysteria?" , "fury" , "Dementia" , "Utter foolishness" .)