"unrelenting" in the adjective sense
1. grim, inexorable, relentless, stern, unappeasable, unforgiving, unrelenting
not to be placated or appeased or moved by entreaty
"grim determination"
"grim necessity"
"Russia's final hour, it seemed, approached with inexorable certainty"
"relentless persecution"
"the stern demands of parenthood"
2. brutal, unrelenting
punishingly harsh
"the brutal summer sun"
"a brutal winter"
3. persistent, relentless, unrelenting
never-ceasing
"the relentless beat of the drums"
Source: WordNet® (An amazing lexical database of English)
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