Conflict causes female to lose stone at first, getting lighter (8)
I believe the answer is:
mismatch
'conflict' is the definition.
(two things in conflict)
'at first getting lighter' is the wordplay.
'at' says to put letters next to each other.
'first getting' becomes 'mis' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'lighter' becomes 'match' (match is a kind of lighter).
'mis' next to 'match' is 'MISMATCH'.
'causes female to lose stone' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for mismatch that I've seen before include "Inappropriate pairing" , "Incompatibility" , "A failure to correspond" , "Mac Smith (anag.)" , "massively uneven contest" .)