Decadal refers to a period of 10 years. There are several synonyms for this term such as "decennial," "ten-yearly," and "per decade." The term "decennary" can also be used in some contexts. These words can be used interchangeably to describe anything that happens every 10 years or lasts for a period of 10 years. For example, decennial census is conducted in the United States every 10 years to gather demographic data. Decadal climatic patterns are closely studied by scientists to understand changes in weather conditions over a period of a decade. All these synonyms have a common meaning and can be used to communicate the same concept effectively.