Aboard a French ship remedy poor energy and sickly condition (13)
I believe the answer is:
unhealthiness
'condition' is the definition.
(unhealthiness is a kind of condition)
'aboard a french ship remedy poor energy and sickly' is the wordplay.
I cannot really understand how this works, but
'aboard' could be 'in' (eg in a vehicle) and 'in' is located in the answer.
'a' is present in the answer.
'ship' could be 'ss' (prefix in ship names eg SS Great Britain) and 'ss' is located in the answer.
'energy' could be 'e' (physics symbol as in E=mc2) and 'e' is present in the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?