This is the 4213th most frequent French word.
décennie
A period of ten years; a decade.
Here, "décennie" is used to refer to a ten-year period in historical context.
La première décennie du XXIe siècle a vu de nombreux changements technologiques.
The first decade of the 21st century witnessed many technological changes.
In this sentence, "décennie" denotes a ten-year duration related to sustained efforts.
Après une décennie d'efforts, ils ont enfin atteint leur objectif.
After a decade of effort, they finally reached their goal.
Here, "décennies" refers to multiple ten-year periods in a broader cultural context.