Insiders love Mum's egg (4)
I believe the answer is:
ovum
'egg' is the definition.
(I've seen this before)
'insiders love mum's' is the wordplay.
I cannot really see how this works, but
'love' could be 'o' (love means zero in tennis) and 'o' is located in the answer.
The remaining letters 'vum' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for ovum that I've seen before include "bit of life potentially" , "Human egg cell" , "A female egg-cell" , "Reproductive cell, 'egg' in Latin" , "Female gamete" .)