ours (pron.)

"that or those belonging to us," c. 1300, oures, a double possessive (with genitive suffix -s (1)), originating in northern England, it has taken over the absolute function of our (q.v.). In Middle English ourn, ouren also were used.

Ours is a later possessive form from our, and is used in place of our and a noun, thus standing to our in the same relation as hers to her, yours to your, mine to my .... [Century Dictionary]