The adverb is a word denoting circumstances or characteristics which attend or modify an action, state, or quality. It may also intensify a quality or characteristics.
From this definition it is difficult to define adverbs as a class, because they comprise a most heterogeneous group of words, and there is considerable overlap between the class and other word classes. They have many kinds of form, meaning and function. Alongside such undoubtful adverbs as here, now, often, seldom, always, there are many others which also function as other word classes. Thus, adverbs like dead (dead tired), clear (to get clear away), clean (I’ve clean forgotten), slow, easy (he would say that slow and easy) coincide with adjectives (a dead body, clear waters, clean hands). Adverbs like past, above are homonymous with prepositions. There is also a special group of pronominal adverbs when, where, how, why used either as interrogative words or as connectives to introduce subordinate clauses.
The adverb is a part of speech characterized by the following features:
1. The lexico-grammatical meaning of “qualitative, quan¬titative or circumstantial characteristics of actions, states or qualities”.
2. The category of the degrees of comparison.
3. Typical stem-building affixes, as in quick-ly, side¬ways, clock-wise, back-wards, a-shore, etc.
4. Its unilateral combinability with verbs, adjectives, adverbs, less regularly with adlinks and nouns.
5. The function of adverbial complement, sometimes other functions.