The phrase "worn thin" refers to something that has become weak or ineffective due to excessive use or overuse. Synonyms for this term include "exhausted," "depleted," "spent," and "overworked." Other phrases that can be used in place of "worn thin" include "worn out," "run down," "burned out," and "used up." Each of these alternatives conveys the idea of something that is no longer effective or useful, either because it has been used too much or because it has reached the end of its useful life. Whether you're writing a report or simply looking for a new way to express an idea, these synonyms can help you convey your message with precision and clarity.