Tenacity
Etymology
From Latin "tenacitas," from "tenax" (holding fast, gripping), from "tenere" (to hold) — the root behind "tenant," "tenure," "retain," and "tenacious." The physical sense of a firm grip is primary; the metaphorical sense of clinging to purposes grew directly from it. A tenacious memory or a tenacious grip both "hold."
noun · /tuh-NASS-uh-tee/
Firm, persistent holding on — to a purpose, a position, or a possession.
What it names
Reach for it to name stubborn grip: the refusal to loosen one’s hold on a goal even when others would let go.
Example
Her tenacity in chasing the records — forty archives, three years — finally broke the story.
Related idea
Perseverance emphasizes pressing forward through hardship; tenacity emphasizes not letting go. The distinction shows at the edges: tenacity, overdone, becomes an inability to release a lost cause, where perseverance implies the cause is still worth pursuing.