tenacious

adjective

1 he paused for a moment, but without releasing his tenacious grip:

firm, tight, fast, clinging;

strong, forceful, powerful, unshakeable, immovable, iron.

▷antonyms loose, weak.

2 he had a reputation for being a tenacious man | a tenacious battle to secure compensation:

persevering, persistent, pertinacious, determined, dogged, single-minded, strong-willed, tireless, indefatigable, resolute, patient, purposeful, diligent, assiduous, sedulous, unflagging, staunch, steadfast, untiring, unwavering, unswerving, unshakeable, unyielding, uncompromising, insistent, importunate, relentless, unrelenting, inexorable, implacable;

stubborn, intransigent, obstinate, obdurate, stiff-necked;

North American rock-ribbed.

▷antonyms irresolute.

3 he had a tenacious memory:

retentive, good;

photographic.

4 she struggled to free herself from the tenacious mud:

sticky, adhesive, clinging, gluey, gummy, glutinous, viscid, viscous, mucilaginous;

British claggy;

Scottish, & Northern English clarty.

tenacious Oxford Dictionary of English