(a.) Not failing; not liable to fail; inexhaustible; certain; sure.

abiding assiduous calculable certain changeless consistent constant continuing dependable devoted diligent dogged durable enduring faithful faithworthy fast firm fixed frozen immobile immutable inalterable indefatigable indomitable industrious insistent intact invariable invincible inviolate lasting loyal marble-constant never-tiring obstinate patient patient as Job permanent perpetual perseverant persevering persistent persisting pertinacious plodding plugging predictable preoccupied quiescent rapt relentless reliable remaining resolute rigid secure sedulous single-minded sleepless slogging solid sound stable static stationary staunch staying steadfast steady stubborn substantial sure surefire sustained tenacious tireless torpid TRUE true-blue trustworthy trusty unabating unaltered unchangeable unchanged unchanging unchecked unconquerable undaunted undestroyed undiscouraged undrooping unfading unfaltering unflagging unflinching unintermitting uninterrupted unnodding unrelaxing unrelenting unremitting unshifting unsleeping unswerving untiring unvaried unvarying unwavering unwearied unwearying unwinking utterly attentive weariless well-founded well-grounded