An adjective (abbreviated ADJ) is a word that describes or defines a noun or noun phrase. Its semantic role is to change information given by the noun. The adjective can be considered one of the main parts of speech of the English language, although historically they were classed together with nouns. Nowadays, certain words that usually had been classified as adjectives, including the, this, my, etc., typically are classed separately, as determiners.

Examples:

Adjective comes from Latin nōmen adjectīvum, a calque of Ancient Greek: ἐπίθετον ὄνομα (surname), romanized: epítheton ónoma, lit. 'additional name' (whence also English epithet). In the grammatical tradition of Latin and Greek, because adjectives were inflected for gender, number, and case like nouns (a process called declension), they were considered a type of noun. The words that are today typically called nouns were then called substantive nouns (nōmen substantīvum). The terms noun substantive and noun adjective were formerly used in English but are now obsolete.

Depending on the language, an adjective can precede a corresponding noun on a prepositive basis or it can follow a corresponding noun on a postpositive basis. Structural, contextual, and style considerations can impinge on the pre-or post-position of an adjective in a given instance of its occurrence. In English, occurrences of adjectives generally can be classified into one of three categories:

Adjectives feature as a part of speech (word class) in most languages. In some languages, the words that serve the semantic function of adjectives are categorized together with some other class, such as nouns or verbs. In the phrase a Ford car, Ford is unquestionably a noun but its function is adjectival (noun adjunct, see below): to modify car.

In some languages adjectives can function as nouns: for example, the Spanish phrase un rojo means 'a red [one]'. This is also possible in English, see above. However, such nominalized adjectives mostly refer to people and are more commonly found in the plural: Reds or a Red (most commonly in the sense of 'communist'), the rich and the famous, the oppressed, the poorer or the poorest, or (not for people) (to venture into) the unknown, the obvious, etc., though use in the singular such as a poor (also the plural (the) poors unlike the poor) or a gay (less so (the) gays) is widely considered dated and generally avoided.

As for "confusion" with verbs, rather than an adjective meaning "big", a language might have a verb that means "to be big" and could then use an attributive verb construction analogous to "big-being house" to express what in English is called a "big house". Such an analysis is possible for the grammar of Standard Chinese and Korean, for example.

Different languages do not use adjectives in exactly the same situations. For example, where English uses "to be hungry" (hungry being an adjective), Dutch, French, and Spanish use "honger hebben", "avoir faim", and "tener hambre" respectively (literally "to have hunger", the words for "hunger" being nouns). Similarly, where Hebrew uses the adjective זקוק‎ (zaqūq, roughly "in need of" or "needing"), English uses the verb "to need".