Adjective and Adverb
English distinguishes between adjectives, which qualify nouns and pronouns, and adverbs, which mainly modify verbs, adjectives, or other adverbs. Not all languages make this exact distinction; many (including English) have words that can function as either. For example, in English, fast is an adjective in "a fast car" (where it qualifies the noun car) but an adverb in "he drove fast" (where it modifies the verb drove).
An adjective is word whose main syntactic role is to modify a noun or noun phrase. Its semantic role is to change information given by the noun.
Adjectives are one of the main parts of speech of the English language, although historically they were classed together with nouns. Certain words that were traditionally considered to be adjectives, including the, this, my, etc., are today usually classed separately, as determiners.
An adverb is a word that modifies a verb, adjective, determiner, clause, preposition, or sentence. Adverbs typically express manner, place, time, frequency, degree, level of certainty, etc., answering questions such as how?, in what way?, when?, where?, and to what extent?. This function is called the adverbial function, and may be realized by single words (adverbs) or by multi-word expressions (adverbial phrases and adverbial clauses).
Adverbs are traditionally regarded as one of the parts of speech. However, modern linguists note that the term "adverb" has come to be used as a kind of "catch-all" category, used to classify words with various different types of syntactic behavior, not necessarily having much in common except that they do not fit into any of the other available categories (noun, adjective, preposition, etc.)