1 : stubbornly unyielding; "dogged persistence"; "dour determination"; "the most vocal and pertinacious of all the critics"; "a mind not gifted to discover truth but tenacious to hold it"- T.S.Eliot; "men tenacious of opinion"
2 : having rugged physical strength; inured to fatigue or hardships; "hardy explorers of northern Canada"; "proud of her tall stalwart son"; "stout seamen"; "sturdy young athletes"
