Synonyms: relentless, unrelenting, persistent
Definition: never-ceasing
Usage: the relentless beat of the drums
Similar words: continual
Definition: occurring without interruption; chiefly restricted to what recurs regularly or frequently in a prolonged and closely spaced series
Usage: the continual banging of the shutters
Synonyms: 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