The phrase "th anniversary" is often used to indicate the number of years since a significant event has occurred. However, there are many synonyms of this phrase that can be used to add variety and interest to your writing. Some alternative phrases that could be substituted include "commemoration," "milestone," "achievement," "jubilee," or "celebration." Each of these terms provides a unique connotation and can help to evoke a different emotional response from the reader. When choosing a synonym for "th anniversary," it's essential to consider the tone and context of your writing to ensure that the phrasing is appropriate.