Crossword Genius

Senior officer’s first sailing-vessel — expensive, they say (9)

Ross

I believe the answer is:

brigadier

'senior officer's' is the definition.
(thesaurus)

I don't understand how the rest of the clue works.

(Other definitions for brigadier that I've seen before include "Rank above colonel" , "Army rank" , "Officer in charge of army unit, part of division" , "High-ranking army officer" , "Military leader" .)

I've seen this clue in The Times.
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