adjective
1.
incapable of being in error
an infallible ear for pitch in music
Synonyms: inerrable, inerrant, sure, unerring
Related Word: faultless, flawless, impeccable, undeceivable; correct, exact, perfect
Contrasted words: deceivable, faulty, unsure; doubtful, dubious, questionable
Antonyms: fallible
2.
not liable to mislead, deceive, or disappoint
an infallible remedy
Synonyms: certain, sure, surefire, unfailing
Related Word: effective, efficacious, efficient; handy, helpful, useful; acceptable, agreeable, satisfying; satisfactory
Contrasted words: doubtful, questionable, uncertain, unsure; useless, worthless; unacceptable, unsatisfying; unsatisfactory
Antonyms: fallible