noun (plural theses /-siːz/)
- 3 /ˈθiːsɪs, ˈθɛsɪs/ Prosody an unstressed syllable or part of a metrical foot in Greek or Latin verse. Often contrasted with arsis.
late Middle English (in sense 3): via late Latin from Greek, literally 'placing, a proposition', from the root of tithenai 'to place'
Make the plural by changing the -is ending to -es: (theses).