Boat captain initially lost authority (6)
I believe the answer is:
oracle
'authority' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for oracle that I've seen before include "Source of divine prophesy" , "Expert" , "Prophesier" , "Holy place where a god was believed to give advice and prophecy" , "One successfully worked" .)