decade-n; 2 Senses

Sense Number 1: a length of time that is ten years

Commentary: DECADE[+quantity][+time][+year][+ten]

That movie was made about a decade ago.
The Soviet Union lasted less than seven decades.
It will take decades for this land to recover.

WordNet 3.0 Sense Numbers: 1

Sense Number 2: any set or group of ten

Commentary: DECADE[+set][+ten]

A division of the Rosary is called a decade.
He sorted the thirty dominos into three decades.

WordNet 3.0 Sense Numbers: 2