determinative

nouns

one of a limited class of noun modifiers that determine the referents of noun phrases
determinative, determiner
a determining or causal element or factor
"education is an important determinant of one's outlook on life"
causal factor, determinant, determinative, determiner, determining factor

adjectives

having the power or quality of deciding
"the crucial experiment"; "cast the deciding vote"; "the determinative (or determinant) battle"
deciding, determinant, determinative, determining