their /ðɝ, ˈðɛr, ˈðær/
Their pron. & a. The possessive case of the personal pronoun they; as, their houses; their country.
Note: ☞ 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.