(ˈ)in, ən+ adjective
Etymology: Medieval Latin infallibilis, from Latin in- in- (I) + Late Latin fallibilis fallible — more at fallible
1. : not fallible : incapable of error : unerring
infallible marksman
infallible ear for pitch in music
infallible memory
2. : not liable to mislead, deceive, or disappoint : sure , certain , indubitable
infallible remedy
his accent is an almost infallible index of his family background and education — Richard Joseph
infallible scheme for making money
3. : incapable of error in defining doctrines touching faith or morals
Synonyms:
inerrable , inerrant , unerring : infallible describes that which is exempt from possibility of error or mistake or that which has been errorless
no mathematician is infallible; he may make mistakes — A.S.Eddington
believed in an infallible Bible — W.W.Sweet
inerrable and inerrant are erudite synonyms for infallible sometimes used in its stead to escape connotations arising from the discussion of papal infallibility; the latter may imply that whatever is described has not so far erred
the Church was ubiquitous, omniscient, theoretically inerrant and omnicompetent — G.G.Coulton
at the moment we lack, in all English-speaking countries, the inerrant literary sense which gave us the Prayer Book Collects, often quite as beautiful in translation as in the original Latin — W.L.Sperry
unerring may imply freedom from error coupled with sureness, reliability, and exactness
an unerring marksman
a man's language is an unerring index of his nature — Laurence Binyon
the unerring scent of the hounds in pursuit — George Meredith