tenacious

Extremely persistent in adhering to or doing something; stubborn or relentless.

Characterized by extreme persistence; relentless or enduring.

Holding together firmly; cohesive.

Clinging to another object or surface; adhesive.

Tending to retain; retentive.

Holding fast, or inclined to hold fast; inclined to retain what is in possession: with of before the thing held; hence, stubborn; obstinate.

Retentive; apt to retain long what is committed to it: said of the memory.

Niggardly; close-fisted.

Apt to adhere to another substance; adhesive, as ropy, glutinous, or viscous matter; sticky; viscid: as, few substances are so tenacious as tar.