Captain Ahab, or his ship (6)
I believe the answer is:
whaler
'captain ahab or his ship' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for whaler that I've seen before include "Tramp across Oz" , "Her law (anag.)" , "Occupation of Melville's Captain Ahab" , "Ship hunting large mammals" , "Ship armed with harpoons" .)