Mum’s abandoned biggest dress (4)
I believe the answer is:
maxi
'dress' is the definition.
(I've seen this before)
'mum's abandoned biggest' is the wordplay.
I cannot quite see how this works, but
'mum' could be 'ma' (both can mean mother) and 'ma' is present in the answer.
The remaining letters 'xi' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for maxi that I've seen before include "Long skirt of coat" , "Full-length skirt" , "Ankle-length skirt" , "racing yacht" , "Long dress" .)