Source : Webster's Revised Unabridged Dictionary (1913)

Tenfold \Ten"fold`\, a. & adv.
   In tens; consisting of ten in one; ten times repeated.

         The grisly Terror . . . grew tenfold More dreadful and
         deform.                                  --Milton.

Source : WordNet®

tenfold
     adj : containing ten or ten parts [syn: {denary}]
     adv : by ten times as much; "the population increased tenfold"