a lot

Very many, a large number; also, very much. For example, A lot of people think the economy is declining, or Sad movies always made her cry a lot. It is sometimes put as a whole lot for greater emphasis, as in I learned a whole lot in his class. It may also emphasize a comparative indication of amount, as in We need a whole lot more pizza to feed everyone, or Mary had a lot less nerve than I expected. [Colloquial; early 1800s]

The adverb has one meaning:

Meaning #1: to a very great degree or extent
  Synonyms: a good deal, a great deal, much, very much