1. An unproved statement put forward as a premise in an argument; a proposition advanced as an argument.
2. A dissertation based on original research; especially, as work toward an academic degree.

Other words for long research papers include: "treatise, dissertation, monograph, disquisition, research, essay", or "investigation".

3. A treatise advancing a new point of view resulting from research; usually a requirement for an advanced academic degree.
4. An "unaccented syllable" or "note", from Latin thesis, "unaccented syllable in poetry"; later "a stressed part of a metrical foot", from Greek thesis, "a proposition"; also, "downbeat" (in music).

Originally, "a setting down" or "placing"; from root of tithenai, "to place, to put, to set".