One-thousandth anniversary, also known as a millennial anniversary, is a significant milestone observed by many people worldwide. However, if you are looking for alternative synonyms, there are several options. For instance, the term millennium is often used to refer to a one-thousandth anniversary celebration. Additionally, one could use the term jubilee, which is often used to refer to any celebration of a significant milestone, regardless of the specific number. Lastly, the phrase "ten centuries" can also be used to refer to a one-thousandth anniversary, as one-thousand years equates to ten centuries. Whether you choose to refer to it as a millennial anniversary, jubilee, or ten centuries, marking such a milestone is an impressive feat worth celebrating.