One's finished working on Hebridean island (7)
I believe the answer is:
retiree
'one's finished working' is the definition.
'on hebridean island' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'hebridean island' becomes 'tiree' (I've seen this before).
're'+'tiree'='RETIREE'
(Other definitions for retiree that I've seen before include "One ceasing to work" , "Someone no longer working" , "Person out of work" , "One no longer working" , "One who has ceased to work" .)