|Origin:||Greek, 'act of laying down', from tithenai 'to put, lay down'|
the‧sis plural theses [countable]
a long piece of writing about a particular subject that you do as part of an advanced university degree such as an MA or a PhD:
Cynthia's still working on her thesis.
He wrote his doctoral thesis on contemporary French literature.
an idea or opinion about something, that you discuss in a formal way and give examples for:
Their main thesis was that the rise in earnings was due to improvements in education.
3 American English
in writing, the thesis is the sentence or group of sentences which state what the main idea of an essay is:
a paragraph introducing your thesis statement