Disturbed rest aboard ship brings tension (6)
I believe the answer is:
stress
'tension' is the definition.
(I know that tension can be written as stress)
'disturbed rest aboard ship' is the wordplay.
'disturbed' indicates an anagram (the order of letters is disturbed).
'aboard' is an insertion indicator.
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'rest' with letters rearranged gives 'tres'.
'tres' inserted into 'ss' is 'STRESS'.
'brings' is the link.
(Other definitions for stress that I've seen before include "Cause of crack" , "Tension - accent" , "Put weight on" , "Emphasise the strain" , "Highlight" .)