The Collaborative International Dictionary of English v.0.48:

Constantly \Con"stant*ly\, adv.
   With constancy; steadily; continually; perseveringly; without
   cessation; uniformly.
   [1913 Webster]

         But she constantly affirmed that it was even so.
                                                  --Acts. xii.
                                                  15.
   [1913 Webster]

WordNet (r) 3.0 (2006):

constantly
    adv 1: without variation or change, in every case; "constantly
           kind and gracious"; "he always arrives on time" [syn:
           constantly, invariably, always]
    2: without interruption; "the world is constantly changing"
       [syn: constantly, always, forever, perpetually,
       incessantly]

Moby Thesaurus II by Grady Ward, 1.0:

89 Moby Thesaurus words for "constantly":
   ad infinitum, again and again, always, at a stretch, at all times,
   at every turn, at regular intervals, at stated times, bona fide,
   ceaselessly, connectedly, consistently, continually, continuously,
   cumulatively, cyclically, daily, daily and hourly, day after day,
   day and night, devotedly, endlessly, eternally, ever,
   ever and anon, everlastingly, every day, every hour, every moment,
   every so often, faithfully, firmly, hour after hour, hourly,
   in good faith, in perpetuity, incessantly, indestructibly,
   infinitely, interminably, intermittently, invariably,
   like clockwork, loyally, methodically, monotonously,
   month after month, never otherwise, never-endingly, night and day,
   on a stretch, on and on, on end, orderly, perdurably, perennially,
   permanently, perpetually, punctually, rapidly, regularly,
   repetitively, responsibly, right along, round the clock, staunchly,
   steadfastly, steadily, sustainedly, systematically,
   time without end, together, unbrokenly, unceasingly, unendingly,
   uniformly, unintermittently, uninterruptedly, unrelievedly,
   unvaryingly, with good faith, without a break, without cease,
   without end, without exception, without letup, without stopping,
   world without end, year after year