treatise
n. countablen. a long and serious piece of writing that explains a subject in great detail. It is usually more formal and deeper than a simple essay.
n. a formal and systematic written discourse on a specific subject, generally longer and more exhaustive than an essay. It aims to present a thorough investigation of principles or facts.
He wrote a long treatise on the history of local architecture.
The professor published a definitive treatise on international law that became a standard text for graduate students.
The philosopher's final work was a dense treatise exploring the intersection of ethics and aesthetics, challenging centuries of established thought on the nature of beauty.
From Middle English tretys, from Anglo-Norman tretiz and Old French traitis (“treatise, account”), from traitier (“to deal with, treat”).
Typically paired with the preposition 'on' to indicate the subject matter.