determinative

(noun) one of a limited class of noun modifiers that determine the referents of noun phrases. Synonyms: determiner.

(noun) a determining or causal element or factor. Synonyms: determinant, determiner, determining factor, causal factor. Example: "Education is an important determinant of one's outlook on life."

(adj) having the power or quality of deciding. Synonyms: deciding(prenominal), determinant, determining(prenominal). Examples: "The crucial experiment." "Cast the deciding vote." "The determinative (or determinant) battle."