Open English Wordnet
Adjectives
(s)dogged, dour, persistent, pertinacious, tenacious, unyieldingstubbornly 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”