Infallible (adjective)

1. Incapable of making a mistake or being wrong.
2. Incapable of failing.
3. Incapable of being deceived or misled.

Origin:

From latin infalli bilis ("unable to deceive, not deceivabl.e")

Examples:

1. The infallible GPS guided the hiker through the wilderness.
2. The Pope is considered infallible in matters of faith and morals.
3. The machine was deemed infallible by its creators, but it broke down after only a month.
4. Infallible in his judgment, the judge never wavered in his decision.
5. The clock's accuracy was infallible, it never varied more than a second in a year.