Go back to basic definitions... In history of university degrees (500 years ago)
A bachelors degree is about learning existing knowledge. Historically from the book(s) written by the univ staff.
A masters degree, after you have learnt what is already known and in books in your topic area, is about learning evolving knowledge - that is near recent and current literature in academic journals and conference presentations.
A doctorate degree is about creating new knowledge by research.
So it is now easy to understand a thesis/dissertation for each degree.
A bachelors degree should be a critique of existing knowledge, often looking for inconsistencies in view points from different sources and synthesising arguments or positions in a DISSERTATION )that is you disserting !
A masters thesis (thesis is Greek for 'I believe') can be either an assembly of new knowledge from new published research or simply a critique and integration. It might have propositions (not hypotheses) that the masters student offers as a conclusion from bringing together new knowledge from different sources.
A doctoral thesis is where the author undertakes research, usually collecting primary new data which is presented as both factual findings and conceptual findings and thus new knowledge in the form of a new model or theory. Also possible, is to challenge existing knowledge and show earlier published knowledge is invalid.
Well that's what they all should be. In practice there is some overlap and different universities and faculties have their own custom and practice. It all starts to break down about 40 years ago when a masters degree become post graduate in time rather than post graduate in level. Thus engineers with a bachelor degree might take an MBA to make them more employable and did more a less a bachelor degree in business in 18 months rather than 3 years as they were already a graduate.
But still thinking in the above categories can help students today focus on the overall agenda.
I have examined over 55 PhD theses. And several hundred masters theses and I base my approach to assessment on the above.
Prof Peter Woolliams, B.Sc(hons), B.A., PhD,
Anglian Ruskin College Cambridge, U K