Determiner (noun)

1. A word, such as "the" or "a" in English, that is used before a noun to indicate the definiteness or indefiniteness of the noun.
2. A word that serves to specify the grammatical function of a following noun, such as a possessive or a demonstrative adjective.

Origin:

Late 16th century: from french déterminer or latin determinare, from de- "completely" + terminare "to limit, fix".

Examples:

1. The determiner "the" is used to indicate specificity.
2. In "the book", the determiner "the" indicates that the speaker is referring to a specific book.
3. The word "a" is an indefinite determiner, indicating that the noun it modifies is one of a group.
4. In "a book", the determiner "a" indicates that the speaker is referring to any book of a group of books.
5. In "my book", the word "my" is a possessive determiner indicating that the book belongs to the speaker.