Tenacity

wiktionary

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tenac(ious) +‎  -ity, from Middle French ténacité, from Latin tenācitās. 

etymonline

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tenacity (n.)

early 15c., tenacite, "quality of holding firmly," from Old French ténacité (14c.) and directly from Latin tenacitas "an act of holding fast," from tenax (genitive tenacis) "holding fast, gripping, clingy; firm, steadfast," from tenere "to hold," from PIE root *ten- "to stretch."