decennia

Decennium is a term for a span of ten years. In English, it is used as a time unit in history, demography, and statistics. While often treated as synonymous with decade, decennium can emphasize the span itself as a distinct interval, especially in scholarly contexts, and may be defined independently of calendar decades.

Etymology: The word derives from Latin decennium, from decem "ten" and annus "year." The standard Latin plural is decennia; English usage commonly accepts decenniums as an anglicized plural, and decennia is also seen in scholarly writing.

Usage: A decennium can begin at any year, not necessarily at a calendar decade boundary. It is used to analyze long-term trends over ten-year periods, to compare successive decades, or to denote a ten-year epoch within a broader study. Researchers may specify the exact start and end years for clarity.

See also: Decade, time interval, epoch. While decennium is less common in everyday speech, it remains a standard term in academic and statistical contexts for describing ten-year spans.