The term 'Infallible Authority' can be summarized by the crossword solution 'ORACLE, ' which is a six-letter word. An ORACLE is a person or agency considered to be an infallible source of wise counsel or prophetic opinion. In ancient Greece, oracles were people believed to be able to provide wise and insightful advice from the gods. In modern times, the term is often used to refer to someone who is seen as an authority on a particular subject.