1treated as singularAn annual international rugby union championship involving England, France, Ireland, Italy, Scotland, and Wales. It was known as the Five Nations until Italy joined in 2000.
2The peoples of the Iroquois confederacy.
Compare with Five Nations (sense 2 of the noun)
Definition of Six Nations in US English:
Six Nations
plural nounsɪks ˈneɪʃənz
the Six Nations
The Five Nations of the original Iroquois confederacy after the Tuscarora joined them in 1722.