Don't tell what we can call Mother! (3'1,3,4)

'don't tell what we can call' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'mother' is the wordplay.
I cannot really see how this works, but
'mother' could be 'mum' (informal term for mother) and 'mum' is found within the answer.
This explanation may well be incorrect...

Can you help me to learn more?