Example : 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.
Men tenacious of opinion.

Synonyms : dogged, persistent, pertinacious, tenacious, unyielding

Example : A dour, self-sacrificing life.
A forbidding scowl.
A grim man loving duty more than humanity.
Undoubtedly the grimmest part of him was his iron claw.

Synonyms : forbidding, grim

Example : A dark scowl.
The proverbially dour New England Puritan.
A glum, hopeless shrug.
He sat in moody silence.
A morose and unsociable manner.
A saturnine, almost misanthropic young genius.
A sour temper.
A sullen crowd.

Synonyms : dark, glowering, glum, moody, morose, saturnine, sour, sullen