Their (?), pron. & a. [OE. thair, fr. Icel. þeirra, þeira, of them, but properly gen. pl. of the definite article; akin to AS. ðāra, ðǣra, gen. pl. of the definite article, or fr. AS. ðǣra, influenced by the Scandinavian use. See That.] The possessive case of the personal pronoun they; as, their houses; their country.
☞ The possessive takes the form theirs (�) when the noun to which it refers is not expressed, but implied or understood; as, our land is richest, but theirs is best cultivated.
Nothing but the name of zeal appears
'Twixt our best actions and the worst of theirs. Denham.