Synonyms of the word

infallible

• adj. Without fault or weakness; incapable of error or fallacy.
• adj. Certain, sure.

foolproof

• adj. For a device: protected, or designed to be proof against misuse or error.
• adj. For an idea or plan: infallible, or bulletproof.
• v. (transitive) To make foolproof.

inerrable

• adj. Incapable of error; infallible.

inerrant

• adj. Of or pertaining to inerrancy. Without error, particularly used in reference to the Bible.

unerring

• adj. (often figuratively) consistently accurate; not missing a target.

unfailing

• adj. inexhaustible.
• adj. changeless.
• adj. infallible.