Four weeks is a common way to denote a month-long period of time, but there are plenty of other phrases and expressions that can also be used to describe the same time frame. These synonyms vary in formality, tone, and context, so it's important to choose the right one for the situation. Some possible synonyms for "four weeks" include "a lunar month," "28 days," "a calendar month," "a fortnight and a half," "a cycle of the moon," and "a month-long span." Additionally, some industries and fields may have their own specific terminology for four-week intervals, such as "billing cycle," "pay period," or "reporting period".