An accountant was an individual who recorded and verified information about the value of assets belonging to an indivdual or organization. Typically this involved money, but could include property as well.
In 2374, Quark claimed to have done business with the "nephew of the cousin of the stepsister of a friend of the secretary to the Consortium's chief accountant". (DS9: "The Magnificent Ferengi")
Nog briefly did accounting work for Vic Fontaine while recovering from the loss of his leg in 2375. He said that as a Ferengi, bookkeeping was in his blood. (DS9: "It's Only a Paper Moon")
Later that year, Ezri Dax told her brother he could leave his work in the family business behind as their mother could pay a real accountant to do the work. (DS9: "Prodigal Daughter")