Moby Dick's pursuer (4)
I believe the answer is:
ahab
'moby dick's pursuer' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ahab that I've seen before include "Captain of the whaler Pequod" , "Name of captain seeking Moby Dick" , "Moby Dick's pursuer" , "Melville's whale chaser" , "Captain in search of Moby Dick" .)