te·na·cious 
(tə-nāshəs)
(tə-nāshəs)adj.
1.
a. Extremely persistent in adhering to or doing something; stubborn or relentless: "tenacious defenders of their harsh and pitiless land" (Dee Brown).
b. Characterized by extreme persistence; relentless or enduring: tenacious detective work; tenacious superstitions.
2. Holding together firmly; cohesive: a tenacious material.
3. Clinging to another object or surface; adhesive: tenacious lint.
4. Tending to retain; retentive: a tenacious memory.
[From Latin tenāx, tenāc-, holding fast, from tenēre, to hold; see ten- in the Appendix of Indo-European roots.]
te·nacious·ly adv.
te·naci·ty (tə-năsĭ-tē), te·nacious·ness n.