Definition - A word that identifies or distinguishes another word without describing or modifying it.

Some types of determiners are:
(1) articles (a, the)
(2) cardinal numbers (three, fifty)
(3) demonstratives (this, those)
(4) indefinite numerals (most, any, each)

Example -

(1) All the men are for themselves.
(2) That man is for himself.

Etymology -
The word determine derives from the Latin determinare, set limits to (from Latin terminus, end or limit).

Oxford English Dictionary -
Its first citation in this sense is from 1933:
"Our limiting adjectives fall into two sub-classes of determiners and numeratives.…"
(Bloomfield Lang. xii. 203)

Please comment