Synonyms of infallible

1 Syllable
sure, true
2 Syllables
correct, handy, sure-fire, come-through, certain, faultless, foolproof, helpful, exact, perfect, flawless, fleckless
3 Syllables
reliable, failsafe, satisfying, inerrant, returnless, watertight, efficient, trustworthy, unfailing, unerring, effectual, agreeable, omniscient, useful
4 Syllables
surefire, acceptable, efficacious, unrefuted, accurate, impeccable, inerrable, inarguable, apodictic, positive, effective, unbeatable
5 Syllables
undisputable, satisfactory, undeceivable, unimpeachable, incontestable, establishable, inevasible, unescapable, unassailable, unquestionable
6 Syllables
authoritative, incontrovertible