(1):

(n.) A familiar for the flagship, or for the principal vessel of a squadron or fleet.

(2):

(n.) A captain commanding a squadron, or a division of a fleet, or having the temporary rank of rear admiral.

(3):

(n.) A title given by courtesy to the senior captain of a line of merchant vessels, and also to the chief officer of a yachting or rowing club.

(4):

(n.) An officer who ranks next above a captain; sometimes, by courtesy, the senior captain of a squadron. The rank of commodore corresponds with that of brigadier general in the army.