adj. 25B6; adjective
his tenacious grip : FIRM, tight, fast, clinging; strong, forceful, powerful, unshakeable, immovable, iron.
a tenacious man : PERSEVERING, persistent, determined, dogged, strong-willed, tireless, indefatigable, resolute, patient, purposeful, unflagging, staunch, steadfast, untiring, unwavering, unswerving, unshakeable, unyielding, insistent; stubborn, intransigent, obstinate, obdurate, stiff-necked; N. Amer. rock-ribbed; formal pertinacious.
weak, irresolute.