What is the meaning of quadruple?

noun

• A set of four similar things considered as a unit.
  • synonyms: quartet, quartette, quadruplet
• A quantity that is four times as great as another.

verb

• Increase fourfold.
  • usage: "His stock earning quadrupled"

adjective

• Having four units or components.
  • usage: "quadruple rhythm has four beats per measure"; "quadruplex wire"
  • synonyms: quadruplicate, quadruplex, fourfold, four-fold
• Four times as great or many.
  • usage: "a fourfold increase in the dosage"
  • synonyms: fourfold, four-fold