What part of speech is the word thesis?

The word "thesis" can be two different parts of speech depending on its usage:

1. Noun: When referring to a long piece of writing, especially one submitted for a university degree, "thesis" is a noun.

Example: "She wrote her thesis on the history of the American Civil War."

2. Adjective: When used to describe something as relating to or based on a thesis, "thesis" functions as an adjective.

Example: "The thesis statement of the essay is clear and well-defined."