Source : Webster's Revised Unabridged Dictionary (1913)

Slipperiness \Slip"per*i*ness\, n.
   The quality of being slippery.

Source : WordNet®

slipperiness
     n 1: a slippery smoothness; "he could feel the slickness of the
          tiller" [syn: {slickness}, {slick}, {slip}]
     2: the quality of being a slippery rascal [syn: {rascality}, {shiftiness},
         {trickiness}]