Aide-de-camp is the title given to a personal assistant, secretary or adjutant to a person of high rank, such as a senior military officer or a head of state.
In 2277, Baroness Commander Amalia served as the aide-de-camp to Starfleet Fleet Admiral Karis Tatenen. (TOS - Star Trek II Short Stories short story: "The Blaze of Glory")
On the planet Vok, Sozz was aide-de-camp to General Gogg. (TOS novel: A Contest of Principles)