as

#21 of the most-used English words

adverb

1. To such an extent or degree; to the same extent or degree.
   "It's not as well made, but it's twice as expensive."
2. Considered to be, in relation to something else; in the relation (specified).
   "1865, The Act of Suicide as Distinct from the Crime of Self-Murder: A Sermon"
3. For example; for instance. (Compare such as.)

preposition

1. Introducing a basis of comparison, with an object in the objective case.
   "They're big as houses."
2. In the role of.
   "He was never seen as the boss, but rather as a friend."

conjunction

1. In the (same) way or manner that; to the (same) degree that.
   "As you wish, my lord!"
2. At the time that; during the time when:
3. Being that, considering that, because, since.
   "As it’s too late, I quit."
4. Introducing a comparison with a hypothetical state (+ subjunctive, or with the verb elided): as though, as if.

Similar: while, whilst, given that, seeing that, albeit, although

noun

1. (unit of weight) A libra.
2. Any of several coins of Rome, coined in bronze or later copper; or the equivalent value.