Only remaining son survives (5)
I believe the answer is:
lasts
'survives' is the definition.
('last' can be a synonym of 'survive')
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for lasts that I've seen before include "Goes on" , "Endures" , "Cobblers' tools" , "Holds out" , "Keeps on" .)