dogged

adjectives

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"
dogged, dour, persistent, pertinacious, tenacious, unyielding
is derived from
doggedness