Expressions of discontent, say, in manuscript (7)
I believe the answer is:
mutters
'expressions' is the definition.
(I have seen 'Expressions of displeasure' mean 'mutters' so perhaps 'expressions' could also mean 'mutters')
'discontent say in manuscript' is the wordplay.
'discontent say' becomes 'utter' (to utter something is to speak or say it. I am not sure about the 'discontent' bit.).
'in' indicates putting letters inside.
'manuscript' becomes 'ms' (abbreviation for manuscript).
'utter' inserted into 'ms' is 'MUTTERS'.
'of' is the link.
Can you help me to learn more?
(Other definitions for mutters that I've seen before include "Expressions of displeasure" , "Grumbles" , "makes unfriendly noises" .)