The Collaborative International Dictionary of English v.0.48:

Incessantly \In*ces"sant*ly\, adv.
   Unceasingly; continually. --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

incessantly
    adv 1: with unflagging resolve; "dance inspires him ceaselessly
           to strive higher and higher toward the shining pinnacle
           of perfection that is the goal of every artiste" [syn:
           endlessly, ceaselessly, incessantly, unceasingly,
           unendingly, continuously]
    2: without interruption; "the world is constantly changing"
       [syn: constantly, always, forever, perpetually,
       incessantly]