What is an acceptable form of their description when referred to as an attributive adjective?

The term being referred to as an attributive adjective is "their" because it functions to show possession or ownership in relation to a noun. In this case, "their" modifies a noun by indicating to whom the noun belongs. For example, in the phrase "their car," "their" is giving information about which car is being spoken of, namely one that belongs to a particular person or group.

In contrast, "thy" is an archaic term for your, "there" is used to indicate a place or to introduce a situation, and "they're" is a contraction for "they are." While these words have specific uses in the English language, they do not function in the same possessive manner as "their," making "their" the only correct answer to describe a possessive form in the context of attributive adjectives.