a period of ten years; a decade. ...

What is the word Decennium mean?

: a period of 10 years : decade.

Which word means a 10 year period?

A decennary is rare word for a ten-year period. In other words, it's a decade. Call a decade a decennary if you're feeling like an old fashioned British lawyer. Like decade and decagon (polygon with ten sides), decennary comes from the Latin root decem for “ten.” A hundred years is made up of ten decennaries.