A catalogue in which all the entries (author, title, subject, series, etc.) and references are arranged in a single alphabet – like a dictionary. As distinct from other alphabetical catalogues, subject entries are made under specific subjects. In some instances, the arrangement of sub-entries may depart from a strictly alphabetical order to provide a logical, or other convenient, arrangement, the main headings still retaining the alphabetical order.
AACR (Anglo American Cataloguing Rules) defines dictionary catalogue as “a catalogue in which all the entries (author, title, subject, series, etc) and their related references are arranged together in one general alphabet, the sub-arrangement frequently varies from strictly alphabetical.” Such a catalogue is called a dictionary catalogue because it is easily usable as a dictionary.