Never-failing is a term used to describe something that is reliable and dependable. The crossword solutions for this term are SURE (4 letters), FOOLPROOF (9 letters), and SUREFIRE (8 letters). SURE is an adjective meaning certain or definite, FOOLPROOF is an adjective meaning impossible to fail or make mistakes, and SUREFIRE is an adjective meaning certain to succeed or be successful. Together, these words all describe something that is dependable and guaranteed to work.