Any member of a class of words that modify nouns and pronouns, primarily
by describing a particular quality of the word they are modifying, as wise in a wise grandmother, or perfect in a perfect score, or handsome in He is extremely handsome. Other terms, as numbers (one cup; twelve months), certain demonstrative pronouns (this magazine; those questions), and terms that impose limits (each person; no mercy)
can also function adjectivally, as can some nouns that are found
chiefly in fixed phrases where they immediately precede the noun they
modify, as bottle in bottle cap and bus in bus station. Synonyms: modifier, qualifier, identifier, describer, describing word.