Gentleman was a title or term of address for a man typically of good conduct or social status.
During the holoprogram The Voyager Encounter, after First Officer Chakotay dismissed Lieutenant Tom Paris' idea of using fighter shuttles in a direct assault against the Kyrians, Paris told Chakotay to propose something of his own to earn his rank. In response, Chakotay angrily struck Paris which resulted in the remaining senior staff getting involved. After Captain Kathryn Janeway's verbal address of the "gentlemen" failed to gain their attention, Janeway proceeded to discharge her phaser. (VOY: "Living Witness")