He's not particular (7)
I believe the answer is:
general
This clue might be a double definition.
'he's' is the first definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'not particular' is the second definition.
(I've seen this in another clue)
Can you help me to learn more?
(Other definitions for general that I've seen before include "top brass" , "Universal" , "Usual; officer" , "Officer < sweeping < public" , "High-ranking officer" .)