Laxative one girl fed to another (8)
I believe the answer is:
magnesia
'laxative' is the definition.
(magnesia can be used as a laxative)
'one girl fed to another' is the wordplay.
I cannot quite understand how this works, but
'one' could be 'i' (Roman numeral) and 'i' is found within the answer.
'girl' could be 'agnes' and 'agnes' is present in the answer.
The remaining letters 'ma' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
(Other definitions for magnesia that I've seen before include "Carbonate used as an antacid" , "laxative" , "Medicinal powder" , "Asian gem (anag) - milk of ___" , "Is Ma easing off the white mineral?" .)