Sea swell aboard cutter (7)
I believe the answer is:
surgeon
'cutter' is the definition.
(surgeons cut into people)
'sea swell aboard' is the wordplay.
'sea swell' becomes 'surge' (I've seen this in another clue).
'aboard' becomes 'on'.
'surge'+'on'='SURGEON'
(Other definitions for surgeon that I've seen before include "Medical knife wielder" , "9 practitioner (through keyhole?)" , "Theatre operator" , "Medical man" , "Medical operator" .)