An unfailing source of strength. The term was originally a religious one, a translation from the Hebrew in the Bible (Isaiah 26:4), which the King James Version has as “everlasting strength.” It later was variously defined as God, religious faith, and salvation. The term became widely known through a hymn of that name published in Gospel Magazine in 1775. Its author, Augustus Montague Toplady, was addressing Jesus when he wrote “Rock of Ages, cleft for me, let me hide myself in Thee.” Subsequently, the term was sometimes used more lightly to describe any highly reliable source of support.