From BiblePortal Wikipedia

Vine's Expository Dictionary of NT Words [1]

1: Τετραπλόος (Strong'S #5073 — Adjective — tetraploos — tet-rap-lo'-os )

an adjective, is found in  Luke 19:8 .

Webster's Dictionary [2]

(1): ( v. t.) To make four times as much or as many, as an assessment,; to quadruple.

(2): ( n.) Four times as many or as much.

(3): ( a. & adv.) Four times; quadruple; as, a fourfold division.

King James Dictionary [3]

Fourfold a. Four double quadruple four times told as a fourfold division.

He shall restore the lamb fourfold.  2 Samuel 12 .

FOURFOLD, n. Four times as much.

International Standard Bible Encyclopedia [4]

fōr - fōld  : Occurs but twice in English Versions:  2 Samuel 12:6 , "He shall restore the lamb fourfold"; and  Luke 19:8 the King James Version, "If I have wrongfully exacted ought ... I restore fourfold." From this statement of Zaccheus we are to understand that fourfold the amount of that which was stolen was the restoration the law required of a thief. This was the extreme penalty the law imposed. In some cases double the amount was to be restored (  Exodus 22:4 ,  Exodus 22:7 ); in others, a fifth of its value was added to the thing restored ( Leviticus 6:5 ); still again, an amount equal to that taken was to be restored ( 1 Samuel 12:3 ).