noun (n)

• how much there is or how many there are of something that you can quantify(noun.tops)

  Synonym:
  amount, measure
  

  source: wordnet30
• an adequate or large amount(noun.attribute)

  Example:
  He had a quantity of ammunition.
  

  source: wordnet30
• the concept that something has a magnitude and can be represented in mathematical expressions by a constant or a variable(noun.cognition)

  source: wordnet30
• The attribute of being so much, and not more or less; the property of being measurable, or capable of increase and decrease, multiplication and division; greatness; and more concretely, that which answers the question "How much?"; measure in regard to bulk or amount; determinate or comparative dimensions; measure; amount; bulk; extent; size.(noun)

  source: webster1913