1. 不顾一切的;不留情面的
If you describe someone's behaviour as unrelenting, you mean that they are continuing to do something in a very determined way, often without caring whether they hurt or embarrass other people.

2. 没完没了的；无休止的
If you describe something unpleasant as unrelenting, you mean that it continues without stopping.

1. never-ceasing

e.g. the relentless beat of the drums

Synonym: persistentrelentless

2. harsh

e.g. the brutal summer sun
a brutal winter

Synonym: brutal

3. 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: griminexorablerelentlesssternunappeasableunforgiving