He's austere and sour about one point (7)
I believe the answer is:
ascetic
'he's austere' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'sour about one point' is the wordplay.
'sour' becomes 'acetic' (I've seen this in another clue).
'about' indicates putting letters inside.
'one point' becomes 'S' (South).
'acetic' going around 's' is 'ASCETIC'.
'and' acts as a link.
Can you help me to learn more?
(Other definitions for ascetic that I've seen before include "Leading a severely simple life without worldly pleasures" , "One practises self-denial as a spiritual discipline" , "One avoiding indulgence" , "Self-denying, often for religious reasons" , "Abstemious, self-denying" .)