“I’ve found that MA students and undergraduates tend to use the term dissertation, and PhD students and DPhil students at Oxford tend to talk of their thesis. It’s almost as though 20,000 words means a dissertation, and 80,000 words is a thesis.”
“I think the meanings of these words are interchangeable. Brian Allison uses the terms synonymously in his book on preparing dissertations and theses. I suppose it all comes down to what language your department uses. But the guidelines – how many words you should you write, what form it should be in, etc – are more important then what you call it.”