Maintains mother doesn't say a word (5,3)
I believe the answer is:
keeps mum
'doesn't say a word' is the definition.
I can't judge whether this definition defines the answer.
'maintains mother' is the wordplay.
'maintains' becomes 'keeps' ('keep' can be a synonym of 'maintain').
'mother' becomes 'mum' (informal term for mother).
'keeps'+'mum'='KEEPS MUM'
Can you help me to learn more?
(Other definitions for keeps mum that I've seen before include "If one behaves filially thus" , "stays silent" .)