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Webster 1828 Edition

adv.

Incessantly; perpetually.

ceaselessly ‎(comparative more ceaselessly, superlative most ceaselessly)

Without ceasing.
- 1905, Richard Jefferies, Nature Near London:
  So the woods are silent, still, and deserted, save by a stray rabbit among the thistles, and the grasshoppers ceaselessly leaping in the grass.

without ceasing