(grammar) A member of a class of words functioning in a noun phrase to identify or distinguish a referent without describing or modifying it. from 1945 Examples of determiners include articles (a, the), demonstratives (this, those), cardinal numbers (three, fifty), and indefinitenumerals (most, any, each).
Something that determines, or helps someone to determine, something else.
1901: Azel Ames, The Mayflower and Her LogThe "steel-yards" and "measures" were the only determiners of weight and quantity — as the hour-glass and sun dial were of time — possessed at first (so far as appears) by the passengers of the Pilgrim ship,