relentless as in 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"

Synonyms

• grimnot to be placated or appeased or moved by entreaty; shockingly repellent; harshly ironic or sinister; harshly uninviting or formidable in manner or appearance; filled with melancholy and despondency; causing dejection
• inexorablenot to be placated or appeased or moved by entreaty; impervious to pleas, persuasion, requests, reason
• sternthe rear part of a ship ; United States concert violinist (born in Russia in 1920) ; the fleshy part of the human body that you sit on; of a stern or strict bearing or demeanor; not to be placated or appeased or moved by entreaty; severe and unremitting in making demands; severely simple
• unappeasablenot to be placated or appeased or moved by entreaty
• unforgivingunwilling or unable to forgive or show mercy; not to be placated or appeased or moved by entreaty
• unrelentingnot to be placated or appeased or moved by entreaty; punishingly harsh; never-ceasing

relentless as in never-ceasing

• "the relentless beat of the drums"

Synonyms

• persistentnever-ceasing; continually recurring to the mind; retained; stubbornly unyielding
• unrelentingnot to be placated or appeased or moved by entreaty; punishingly harsh; never-ceasing