Trimestril

Trimestril is a term used in discussions of calendar design and speculative worldbuilding to denote a unit of time equal to three months. It is not an officially recognized unit in standard timekeeping systems, such as the Gregorian calendar or international time standards, and it does not have formal status in civil, scientific, or financial calendars.

The word appears to be a coinage combining the prefix tri- (three) with a suffix that resembles other time-related terms, though there is no single authoritative spelling or origin. In most uses, trimestril is described as a three-month block that can serve as a basic division of the year in alternative calendars or fictional settings. Because it is not standardized, the exact length can vary: in fixed-calendar models it is typically four quarters per year, while in flexible models the length may be aligned with three consecutive calendar months, which creates minor variations in total days year to year.

Common use cases for the concept include academic terms, fiscal planning, and worldbuilding where a year is partitioned into equal multi-month segments. Proponents argue that three-month blocks simplify planning and align with seasons in some cultural contexts, while critics note potential mismatches with lunar cycles, seasonal definitions, and existing quarterly systems in business and government.

Related concepts include trimester, quarter, semester, and fiscal quarter. Trimestril remains primarily a theoretical or fictional construct rather than a widely adopted time unit.