Plurals

Q. Greetings from New Zealand. May I please ask you what is the plural of “thesis” and whether this word is of Latin or Greek origin? Many thanks.

A. For this sort of thing, we at the University of Chicago Press must rely on the lexicographers. According to Merriam-Webster, the plural is “theses” and the origin is Greek.

[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]