1. 不停的;不懈的;不间断的；未减轻的
Something bad that is relentless never stops or never becomes less intense.

1. never-ceasing

e.g. the relentless beat of the drums

Synonym: persistentunrelenting

2. not to be placated or appeased or moved by entreaty

e.g. grim determination
grim necessity
Russia's final hour, it seemed, approached with inexorable certainty
relentless persecution
the stern demands of parenthood

Synonym: griminexorablesternunappeasableunforgivingunrelenting