In grammar, an adjective is a 'describing' word; the main syntactic role of which is to qualify a noun or noun phrase, giving more information about the object signified.
Adjectives are one of the traditional eight English parts of speech, though linguists today distinguish adjectives from words such as determiners that were formerly considered to be adjectives. In this paragraph, "traditional" is an adjective, and in the preceding paragraph, "main" and "more" are.
Most but not all languages have adjectives. Those that do not, typically use words of another part of speech, often verbs, to serve the same semantic function; for example, such a language might have a verb that means "to be big", and would use a construction analogous to "big-being house" to express what English expresses as "big house".
Even in languages that do have adjectives, one language's adjective might not be another's; for example, whereas English uses "to be hungry" (hungry being an adjective), Dutch and French use "honger hebben" and "avoir faim," respectively (literally "to have hunger", hunger being a noun), and whereas Hebrew uses the adjective "זקוק" (zaqūq, roughly "in need of"), English uses the verb "to need".
Adjectives form an open class of words in most languages that have them; that is, it is relatively common for new adjectives to be formed via such processes as derivation. However, Bantu languages are well known for having only a small closed class of adjectives, and new adjectives are not easily derived. Similarly, native Japanese adjectives (i-adjectives) are a closed class (as are native verbs), though nouns (which are open class) can be used in the genitive and there is the separate class of adjectival nouns (na-adjectives), which is also open, and functions similarly to noun adjuncts in English.
An adjective modifies a noun or a pronoun by describing, identifying, or quantifying words. An adjective usually precedes the noun or the pronoun which it modifies.
In the following examples, the highlighted words are adjectives:
The truck-shaped balloon floated over the treetops.
Mrs. Morrison papered her kitchen walls with hideous wall paper.
The small boat foundered on the wine dark sea.
The coal mines are dark and dank.
Many stores have already begun to play irritating Christmas music.
A battered music box sat on the mahogany sideboard.
The back room was filled with large, yellow rain boots.
Comparative adjectives are only used to compare the difference between only 2 nouns.
