The Collaborative International Dictionary of English v.0.48:

Rampancy \Ramp"an*cy\ (r[a^]mp"an*s[y^]), n.
   The quality or state of being rampant; excessive action or
   development; exuberance; extravagance. "They are come to this
   height and rampancy of vice." --South.
   [1913 Webster]