The word "tenacious" is defined as "holding firmly or stubbornly to a purpose, cause, or belief." Some synonyms for tenacious include persistent, steadfast, determined, indomitable, unwavering, resolute, unyielding, dogged, unrelenting, and adamant. These words can be used interchangeably with tenacious depending on the context of the sentence. For example, instead of saying "He was tenacious in his pursuit of success," one could say "He was persistent in his pursuit of success" or "He was dogged in his pursuit of success." All of these synonyms highlight the undeterred determination and dedication of the individual.