The Collaborative International Dictionary of English v.0.48:

Eternally \E*ter"nal*ly\, adv.
   In an eternal manner.
   [1913 Webster]

         That which is morally good or evil at any time or in
         any case, must be also eternally and unchangeably so.
                                                  --South.
   [1913 Webster]

         Where western gales eternally reside.    --Addison.
   [1913 Webster]

WordNet (r) 3.0 (2006):

eternally
    adv 1: for a limitless time; "no one can live forever";
           "brightly beams our Father's mercy from his lighthouse
           evermore"- P.P.Bliss [syn: everlastingly, eternally,
           forever, evermore]

Moby Thesaurus II by Grady Ward, 1.0:

38 Moby Thesaurus words for "eternally":
   ad infinitum, always, boundlessly, ceaselessly, constantly,
   continually, endlessly, ever, everlastingly, evermore, forever,
   forevermore, illimitably, immeasurably, immensely, in perpetuity,
   incalculably, incessantly, incomprehensibly, indestructibly,
   infinitely, innumerably, interminably, limitlessly, measurelessly,
   never-endingly, perdurably, perennially, permanently, perpetually,
   steadily, time without end, to infinity, unceasingly, unendingly,
   without end, without limit, world without end