unflinching (adj.)

• assiduous
• balanced
• calm
• constant
• continuing
• cool
• coolheaded
• diligent
• dogged
• enduring
• faithful
• fast
• fiducial
• firm
• immutable
• imperturbable
• implacable
• inalterable
• indefatigable
• indomitable
• industrious
• insistent
• invincible
• lasting
• loyal
• merciless
• mortal
• nerveless
• obstinate
• patient
• permanent
• persevering
• persistent
• persisting
• pertinacious
• plodding
• predictable
• preoccupied
• rapt
• relaxed
• relentless
• reliable
• resolute
• rock-steady
• ruthless
• secure
• sedulous
• single-minded
• sleepless
• solid
• sound
• stable
• steadfast
• steady
• stubborn
• substantial
• tenacious
• tireless
• unabashed
• unappeasable
• unawed
• unblinking
• unconquerable
• undaunted
• undiscouraged
• undismayed
• unfailing
• unfaltering
• unflagging
• unflappable
• unhesitating
• uninterrupted
• unintimidated
• unrelenting
• unremitting
• unshakable
• unshaken
• unshrinking
• unsleeping
• unstrained
• unswerving
• untiring
• unwavering
• unwearied
• unwearying
• unyielding
• well-balanced