Cure on sea at journey's end (6)
I believe the answer is:
remedy
'cure' is the definition.
(I know that cure can be written as remedy)
'on sea at journey's end' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'sea' becomes 'med' (short for Mediterranean).
'at' says to put letters next to each other.
'end' suggests the final letters.
The last letter of 'journey' is 'y'.
're'+'med'+'y'='REMEDY'
(Other definitions for remedy that I've seen before include "answer" , "Nostrum" , "fix" , "Something that cures, disease or problem" , "A cure, for disease or other ill" .)