quadruple

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Consisting of four parts or members.
• adjective Four times as much in size, strength, number, or amount.
• adjective Music Having four beats to the measure.
• noun A fourfold amount or number.
• transitive & intransitive verb To multiply or be multiplied by four.

from The Century Dictionary.

• To make four times as much or as many; multiply by four; repeat four times; make, do, or cause to happen four times over.
• To become four times as much or as many; repeat itself four times.
• Consisting of four parts; completed in four separate or successive operations.
• Fourfold; four times told.
• noun A number, sum, etc., four times as great as that taken as the standard: as, to receive the quadruple of a given sum.

from the GNU version of the Collaborative International Dictionary of English.

• noun four times the sum or number; a fourfold amount.
• adjective Fourfold
• adjective (Mus.) that in which each measure is divided into four equal parts.
• intransitive verb To be multiplied by four; to increase fourfold; to become four times as much.
• transitive verb To multiply by four; to increase fourfold; to double; to double twice.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Being four times as long, as big or as many of something.
• verb To multiply something by four times.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb increase fourfold
• adjective having four units or components
• noun a quantity that is four times as great as another
• noun a set of four similar things considered as a unit
• adjective four times as great or many