The Collaborative International Dictionary of English v.0.48:

Endlessly \End"less*ly\, adv.
   In an endless manner.
   [1913 Webster]

WordNet (r) 3.0 (2006):

endlessly
    adv 1: continuing forever without end; "there are infinitely
           many possibilities" [syn: infinitely, endlessly]
           [ant: finitely]
    2: 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]
    3: (spatial sense) without bounds; "the Nubian desert seemed to
       stretch out before them endlessly"
    4: all the time; seemingly without stopping; "a theological
       student with whom I argued interminably"; "her nagging went
       on endlessly" [syn: interminably, endlessly]