Source : Webster's Revised Unabridged Dictionary (1913)

Incessancy \In*ces"san*cy\, n. [From {Incessant}.]
   The quality of being incessant; unintermitted continuance;
   unceasingness. --Dr. T. Dwight.

Source : WordNet®

incessancy
     n : the quality of something that continues without end or
         interruption [syn: {continuousness}, {ceaselessness}, {incessantness}]