Main entry: relentless, unrelenting, persistent
Definition: never-ceasing
Usage: the relentless beat of the drums
Main entry: brutal, unrelenting
Definition: harsh
Usage: the brutal summer sun; a brutal winter
Main entry: inexorable, grim, unrelenting, relentless, unappeasable, unforgiving, stern
Definition: not to be placated or appeased or moved by entreaty
Usage: grim determination; grim necessity; Russia's final hour, it seemed, approached with inexorable certainty; relentless persecution; the stern demands of parenthood