1. incapable of making mistakes or being wrong
2. never failing; completely reliable

Examples

• No human being is infallible.
• The GPS system seemed infallible until it led us down a dead-end road.
• She had an infallible memory for faces and names.
• The detective’s infallible instincts helped solve the case.
• Many people once believed the encyclopedia was an infallible source of information.
• His infallible technique made him the best surgeon in the hospital.