1) By a factor of four 2) Four times as great or many 3) Multiple 4) Quadruple 1) Multiple 2) Quadplex 3) Quadruple 4) Quadruplex 5) Quadruplicate 
• (v. t.) To make four times as much or as many, as an assessment,; to quadruple. • (n.) Four times as many or as much. • (a. & adv.) Four times; quadruple; as, a fourfold division.
Four'fold` adjective & adverb [ Anglo-Saxon feówerfeold .] Four times; quadruple; as, a fourfold division. « He shall restore the lamb fourfold .» 2 Sam. xii. 6. Four'fold` noun Four times as many or as much. Four'fold` transitive verb To make four times as much or as many, as an assessment; to quadruple. 
[adv] - by a factor of four
four times adverb by a factor of four; `the price of gasoline has increased fourfold over the past two years`
comprising four parts or members. · four times as great or as much.