Here are some synonyms for tenacious:
* Persistent
* Determined
* Resolute
* Unwavering
* Relentless
* Dogged
* Stubborn (can have a negative connotation)
Here are some examples of how "tenacious" can be used:
* "She was a tenacious negotiator and refused to settle for anything less than the best deal."
* "The tenacious athlete kept training even after multiple injuries."
* "Despite the challenges, he held onto his tenacious belief in a brighter future."
In short, someone who is tenacious shows a strong commitment and dedication to achieving their goals, even in the face of difficulties.