as

As is a versatile English function word with several grammatical roles. It can act as a conjunction, a preposition, or an adverb, and it is commonly used to express time, cause, manner, comparison, and role. Its broad range of meanings makes it a frequent item in both spoken and written language.

As a conjunction, as introduces subordinate clauses. It can signal time (As we arrived, the show began), cause (As it was late, we left), or manner and condition (Do it as I showed you). It also appears in comparative expressions, notably in correlative forms like as...as to express equality (as tall as the tallest person) and in phrases such as as if and as though to indicate imagined similarity or conjecture.

As a preposition, as marks function or role, as in She worked as a consultant. It also appears in a variety of set phrases, including as of (starting from a date), as well as (in addition to), and as for (concerning). These uses help connect a noun phrase to its context or specification.

As an adverb or degree word, as can modify adjectives and adverbs within both simple and correlative comparisons. Common examples include as big as, as quickly as, and phrases such as not as … as (less than) or as soon as (immediately). In many contexts, as part of a larger construction (as soon as, as long as), it helps convey timing or condition.

Etymology traces as to the Old English period, with cognates in other Germanic languages (for example Dutch als, German als, Swedish som). It remains highly polyfunctional and essential for precise expression across registers.