Agree to take part with mother withholding name? That’s for the best (7)
I believe the answer is:
optimum
'for the best' is the definition.
(I've seen this before)
'agree to take part with mother withholding name?' is the wordplay.
I cannot quite see how this works, but
'part' could be 'ti' (ti is a kind of part) and 'ti' is found within the answer.
'mother' could be 'mum' (informal term for mother) and 'mum' is found in the answer.
The remaining letters 'op' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'that's' is the link.
(Other definitions for optimum that I've seen before include "Best (result)" , "Most appropriate" , "The most favourable condition" , "The best possible" , "Most favourable point" .)