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" ;