relentless
1. [ adjective ] not to be placated or appeased or moved by entreaty
Synonyms: grim stern inexorable unforgiving unrelenting unappeasable
Examples:

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

Related terms: implacable
2. [ adjective ] never-ceasing
Synonyms: persistent unrelenting
Examples:

"the relentless beat of the drums"

Related terms: continual
Similar spelling:   relentlessly