Definitions
from The American Heritage® Dictionary of the English Language, 4th Edition
 adj. Consisting of ten parts or members.
 adj. Ten times as much in size, strength, number, or amount.
 n. A tenfold amount or number.
 transitive v. To multiply or be multiplied by ten.
from Wiktionary, Creative Commons Attribution/ShareAlike License
 adj. Ten times as much.
 n. An amount multiplied by ten.
 v. To multiply by ten.
from the GNU version of the Collaborative International Dictionary of English
 adj. Tenfold.
 n. A number ten times repeated.
 transitive v. To make tenfold; to multiply by ten.
from The Century Dictionary and Cyclopedia
 Tenfold; containing ten times as many.
 n. A number ten times repeated.
 To increase tenfold.
Etymologies
Examples

With decuple vigour the stench now rose close to hand.

And so oft do away þe lasse nounbre out of his owne decuple, þat is to say, fro þat nounb {r} e þat is ten tymes so mych is þe nounb {re} þ {a} t comes of þe m {u} ltiplicacioɳ.

The truth simply is that if some remedy be not soon found for the situation created by these people, who are as stupid as they are mischievous, in a few years we shall be obliged either to decuple the gendarmerie, or to allow every citizen to go about armed with a revolver, in order to protect himself against our much too liberally emancipated young scolos! '

But as the Franks established only a decuple proportion of gold and silver, ten shillings will be
History of the Decline and Fall of the Roman Empire — Volume 3

But as the Franks established only a decuple proportion of gold and silver, ten shillings will be a sufficient valuation of their solidus of gold.

Hence it appears, that Cyphers put on the Right  hand of whole Numbers, do increafe the Value of thofe Numbers in a decuple (or tenfold) Proportion:
The Complete Measurer: Or, The Whole Art of Measuring. In Two Parts. The First Part Teaching ...

[[written cubik {e} ...]] +decuple+, 22/12; the product of a number by ten.

C {er} ten þ {ere} wel be vj vnitees bytwene 4 & ten. yf þ {o} u reken þ {ere} w {i} t {h} þe ten þe vnite, as þou may se. so mony tymes take 2. out of his decuple, þe quych is 20. for 20 is þe decuple of 2, 10 is þe decuple of 1, 30 is þe decuple of 3, 40 is þe decuple of

And, en (he contrary, thoMn whole Numbers, Cyphers pre  fixed before them, do neither increafe nor diminilb the Value; yet Cyphers before a decimal Fraction do diminiih its Value in a decuple Proportion: For .25, if yon prefix a Cypher before it, becomes t%%'o oc
The Complete Measurer: Or, The Whole Art of Measuring. In Two Parts. The First Part Teaching ...
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hernesheir commented on the word decuple
Based upon the 10root dec, as in decade. Not to be confused with decouple.
December 15, 2011