Disquisition, n.
Etymology: [L. disquisitio, fr. disquirere to inquire diligently, investigate; dis- + quaerere to seek. See Quest.]
A formal or systematic inquiry into, or discussion of, any subject; a full examination or investigation of a matter, with the arguments and facts bearing upon it; elaborate essay; dissertation. For accurate research or grave disquisition he was not well qualified. Macaulay.
Shades of meaning
Fernald has no entry of its own for disquisition; he lists it under speech.
He lists it without comment; the entries above explain its neighbors.