The phrase "one-twelfth of a year" is often used to refer to a month. However, there are several synonyms that can be used interchangeably. For example, "a lunar cycle" refers to the time it takes for the moon to go through all its phases, which is also about one-twelfth of a year. "30 days" is another synonym, as most months have approximately 30 days. "Four weeks" is also a common synonym, as there are usually four complete weeks within a month. It's important to note that some months have slightly different lengths, but these synonyms generally refer to a standard month.