Noun

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

Adjective

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