Determinative

Part of speech: noun (n.)

That which serves to determine. Explanatory determinatives . . . were placed after words phonetically expressed, in order to serve as an aid to the reader in determining the meaning. I. Taylor (The Alphabet).

Part of speech: adjective (a.)

Having power to determine; limiting; shaping; directing; conclusive. Incidents . . . determinative of their course. I. Taylor. Determinative tables (Nat. Hist.), tables presenting the specific character of minerals, plants, etc., to assist in determining the species to which a specimen belongs.