'Tenacious' is Latin for 'holding fast' — from 'tenere' (to hold). Gripping and not letting go.
Tending to keep a firm hold of something; persistent and determined; not readily letting go or giving up.
From Latin 'tenāx' (holding fast, gripping, stubborn — genitive 'tenācis'), from 'tenēre' (to hold, to grasp, to keep possession of), from PIE *ten- (to stretch, to hold firm, to extend). The PIE root *ten- is extraordinarily productive across the Indo-European family: it underlies 'tendon' (the tissue that holds muscle to bone), 'tense' (held, stretched), 'tender' (stretched thin), 'tenor' (the held note, the sustained voice), 'tenant' (one who holds land), 'sustain' (to hold up from below), 'obtain' (to hold toward oneself), 'retain' (to hold back), and Greek 'teinō' (to stretch). Latin 'tenāx' was a strong word: it described the grip of a fighter
The tool called 'tenaculum' (a surgical instrument with a sharp hook for grasping tissue) and 'tenon' (the projecting piece of wood that fits into a mortise) both come from the same Latin root. A tenaculum holds tissue; a tenon holds a joint together. The root 'tenēre' spread through technologies of holding — from the human hand