Old English tretis, Old French treitis, traitis, well made. See Treat.
  • A written composition on a particular subject, in which its principles are discussed or explained; a tract. Chaucer.
    He published a treatise in which he maintained that a marriage between a member of the Church of England and a dissenter was a nullity.
    — Macaulay.
    ☞ A treatise implies more form and method than an essay, but may fall short of the fullness and completeness of a systematic exposition.
  • [Rare] Story; discourse. Shakespeare