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Synonyms for Unrelenting (same or very similar meaning)

WordNet sense 1 (not to be placated or appeased or moved by entreaty):
grim, inexorable, relentless, stern, unforgiving, unappeasable

WordNet sense 2 (incapable of being placated):

WordNet sense 3 (never-ceasing):

WordNet sense 4 (seemingly without interruption; chiefly restricted to what recurs regularly or frequently in a prolonged and closely spaced series):

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