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"
characterized by care and perseverance in carrying out tasks; "a diligent detective investigates all clues"; "a diligent search of the files"
quietly and steadily persevering especially in detail or exactness; "a diligent (or patient) worker"; "with persevering (or patient) industry she revived the failing business"
not easy; requiring great physical or mental effort to accomplish or comprehend or endure; "a difficult task"; "nesting places on the cliffs are difficult of access"; "difficult times"; "a difficult child"; "found himself in a difficult situation"; "why is it so hard for you to keep a secret?"
requiring much effort and trouble; "the mountain climb was long, steep, and difficult"